Saying "You're screwed if you buy this when you already have the current gen version" is like saying Rockstar screwed you over for buying Bully: Scholarship edition on 360 when you already have the PS2 Version.
Rockstar developed GTA V with the 360 and PS3 in mind, judging from the files they were already working on a PC version from the get go. It just so happens that they wanted to develop on the next-gen versions because they had the PC version as a foundation to build upon. Nobody's forcing you to purchase the next-gen version and it's up to you if you want to upgrade.
Also, if they announced a next-gen version along with the current gen version then nobody would've bought the 360/PS3 version and all that work and man hours would've gone to waste.
I agree with pretty much everything here.