For people who actually would consider 1 TB, having 6 GB (even if not advertised) is even more of an incentive to spend the $$$$.On a device where they don't advertise RAM specs as an upsell?
I expect there's a technical reason 1TB got more RAM. I do think it got more than was necessary and that even the extra 512MB it would have needed over the lower end models, the storage doesn't require all the time hence, the extra 2GB is more often than not usable by all apps.
BTW, we’ve been using 1 TB drives with our 4 GB computers for well over a decade now. It’s just that they used to be hard drives and now they are SSDs.
Regardless, the bigger point for me is that it tells developers and us indirectly that 6 GB is the new target for iOS. I take that to mean that for the iPad Pros, we will get 6 GB across the board sooner rather than later.