I would agree the HD4000 is not faster. I've been stating all along that that the HD4000 is more or less an equal of the 6630M. My point was simply that while, in the benchmarks you pointed out, that the 6630M did beat the HD4000 they are both in essence the same Tier/class of GPU (i.e. they both run software at relatively the same speed). It's like anything else, an entry level Nvidia will beat and Entry level AMD at some games, and vice versa. You would still consider them equals because of this.
I will agree with those who are disappointed that in a year+ we ended up with Mac Mini's that have the same GPU "power" as the previous Mid-Level Mac mini, but truthfully the 2011 Mid-Mini was the only Intel Mini to have a discrete GPU and my guess is that was only because the HD3000 was so lackluster. I'm just glad that the HD4000 is such a step up and can't wait for the GPU in Haswell which is probably when I will upgrade my 2011 MBA and 2011 Mac Mini....
I agree that the GPU differences are academic. But as you rightly acknowledge, after a timespan of 1yr+, for some more tech-savvy consumers these latest updates disappoint.
Mind, not hard to see why they've done it (beyond that they can do & still achieve VG sales!).
Rather than making the Mini a bit more attractive to those who value a slight upgrade in GPU power, it's allowed Apple to actually downgrade the graphical power of low-end iMacs, but without compromising sales of a more profitable product, as the iMac is.
FWIW, that also gets plenty of criticism on some iMac threads from those prepared to see beyond the sheer thinness of the latest iMacs, but I won't go there as I have no interest in buying another iMac.
FWIW, new low-end iMac's GT 640M scores 1394, whilst former low-end HD 6750 scores a more impressive, 1614:
http://www.videocardbenchmark.net/high_end_gpus.html
I'm well aware of current BTO options for a significantly higher price, but that's not relevant to this point.
Also, probably far cheaper to buy only HD 4000 boards in bulk for current Mini production lines, rather than split them & improve the older HD 6630M with a better discrete card & double the VRAM to 512.
Outwardly it's a clever business calculation from Apple to maximize profits further as most consumers won't care. However, it'll also cost them sales from others.
For eg., a fair number like me would've have gladly upgraded our HD 6630M Minis far sooner. Now I won't be doing so for a long time, but will spend that extra money on upgrading my PC hardware.
Apple won't care of course & ultimately neither will I, but the original point stands.