Can probably get close with less bandwidth.
That's what "scratches its back" actually implies.
Then again you'd wonder why if the chip had more potential they'd cripple it so.
Probably in order to fit into the specific performance price/performance league. In such a case it's not "crippled" at all, especially if the rumored MSRP for it is correct. A $300 SKU isn't obviously high end, since high end will be in a completely different price/performance league.
Counter-question: the 7970 looks like an outstanding overclocker. Any idea why AMD didn't clock it at say 1.0 or even 1.1GHz? You'd take vendors some part of their business out of their hands, overclockers won't have as much a joyride as right now and the performance gap to the 7990 inevitably shrinks. Is the TahitiXT in that regard "crippled"? It's IMHO clocked at its sweet spot the majority of aspects encounted.