Good and informative post, compuwar. I learned a lot reading it.
I shouldn't be so harsh toward the D40 and its brethren. After all, I had one myself for a time. Its pixel size is very large, beneath only the D3/x/700.
You didn't mention, though, that until the 35mm 1.8 came along, there was virtually no option for wide angle primes within Nikon's lineup for D40/60 users to autofocus with, and there still isn't much of one at this moment. The 14mm, 18mm, 20mm, 24mm, and 28mm are all AF-D lenses.
The 14mm doesn't do well on digital and is so much more expensive than the camera that it's simply not a likely purchase- even on film where it worked well it wasn't a hugely popular purchase. I don't think I've ever known anyone who had an 18mm, even in the film days- but at both those focal lengths autofocus isn't really that critical for most shots anyway.
Sigma's been offering primes, Nikon's been offering zooms- Nikon really doesn't expect the beginning photographer to want a bunch of limited focal length lenses, hence their priority has been in improving the consumer-grade zooms rather than replacing older short focal length lenses. Nikon's actually somewhere between 1.6 and 1.8 lenses a customer, so they've been selling more lenses to more customers than the average DSLR manufacturer (which lived at 1.2-1.3 for the longest time) mostly due to ultra long zooms like the 18-200 and two-lens kits, so you can see why they're not in a rush to spend resources on lenses that aren't selling and haven't traditionally sold in significant numbers.
Their formula is so successful that (a) they overcut production on most of their products when the economy nosedived and (b) they're increasing per-camera lens sales and (c) they've gained more market share than any other manufacturer and (d) they made a (small) profit on their DSLR business when pretty-much *everyone* else lost money. They're not going to change a winning formula without a lot of good reasons.
Sigma offers a lot of fixed focal length lenses that will AF with the D40 and are likely about as good as the older AF-D Nikkors, including:
4,5mm f/2,8 EX DC HSM
10mm f/2,8 EX DC HSM
14mm f/2.8 EX
30mm f/1.4 EX DC HSM
50mm f/1.4 EX DG HSM
In the much more popular wide angle zoom category you get:
Tokina:
12-24 f/4 AT-X 124 PRO DX II
Tamron:
10-24mm f/3.5-4.5 Di II LD New
17-50mm f/2.8 XR Di II
18-250mm f/3.5-6.3 Di II
18-270mm f/3,5 -6,3 Di II VC LD
Sigma:
10-20mm f/4-5.6 EX DC HSM
10-20mm f3,5 EX DC HSM
12-24mm f/4.5-5.6 EX DG HSM
17-35mm f/2.8-4.0 EX DG
17-70mm f/2.8-4.5 DC Macro HSM
18-50mm f/3.5-5.6 DC HSM
18-50mm f2,8-4,5 DC OS HSM
18-50mm f/2.8 EX DC Macro HSM
18-125mm f/3.8-5.6 DC OS HSM
18-200mm f/3.5-6.3 DC OS
18-250mm f3.5-6.3 DC OS HSM
24-70mm f2,8 EX DG HSM
Nikon:
AF-S DX 10-24mm f/3,5-4,5 ED G
AF-S DX 12-24mm f/4.0G ED-IF
AF-S 14-24 mm f/2,8G ED
AF-S DX 16-85mm f/3,5 - 5,6G ED VR
AF-S 17-35mm f/2.8D ED-IF
AF-S DX 17-55mm f/2.8G ED-IF
AF-S DX 18-55mm f/3.5-5.6G
AF-S VR DX 18-55mm f/3.5-5.6G
AF-S DX 18-70mm f/3.5-4.5G ED-IF
AF-S VR DX 18-105 f/3.5-5.6G ED
AF-S DX 18-135mm f/3.5-5.6 ED-IF
AF-S VR DX 18-200mm f/3.5-5.6G IF-ED
AF-S 24-70 mm f/2,8G ED
AF-S 24-85mm f/3.5-4.5G IF-ED
AF-S VR 24-120mm f/3.5-5.6G ED-IF
I'd bet even money that the 14-24mm outperforms the old 14mm, the 20mm and the 24mm AF-D primes wide open through most of its range (but I can't even really be bothered to hunt down the MTFs, my old 20-35mm AF-D is at least as good as the 24mm, and probably the 20mm too.) If there was a significant market for wide primes, you'd see more than Sigma making them. So, if you look, you can see everyone's doing wide and ultra-wide angle zooms. Modern zooms are a fairly good argument against primes until you get over about 200mm- and low-cost zooms that go with low-cost cameras are more attractive to more buyers than expensive primes, no matter what their focal length. Nikon will replace or kill their AF-D lenses once they're out of stock- but if you look at the number of manual focus lenses that Nikon still offers today, you can see that it may be quite a while until they retire the whole catalog.
Nikon's been doing a fair job of upgrading and adding to the lens catalog where it makes sense (despite the overabundance of overlapping consumer zooms- which are really a testament to them wanting to improve their low-end offerings no matter what-- remember it wasn't more than a couple of years ago where Canon's kit lenses sucked ear wax and Nikons were still pretty decent.) Remember that Canon owned the tilt/shift space for the longest time and Nikon's pretty-much offering as many options now- and those are low-volume sales lenses.
I own three primes- 24mm, which I *never* shoot with, 300mm/4, which has been loaned out for a few years now, and 400mm which I shoot a lot with. My wide angle needs are met with a Sigma 10-20mm, and a Nikkor 20-35mm which gets little use, and most of the time I'm in manual focus with it anyway. My wish list for primes is 200mm micro, 85/1.8 and either the 105 Micro or a Tamron 90mm macro- because I don't think a wide prime is going to get me any significant detail increase in anything that I can't shoot and stitch with a closer lens. There may be a market for wide primes, but frankly if there were, Sigma couldn't keep that 30mm on the shelves as it's at a great price for a fast/wide prime.
Our budding photographer isn't going to miss a focal length, and so all they're going to miss is shallow depth of field and low light capability- you have to pay to get those, though they're cheaper and better than they've ever been in history. You want sub 4-second 0-60, you're not going to get that on a budget either, no matter how cool you think the new cars look... It's still cheaper and more available than ever though.