It wouldn't be the first time. G71 was 2/3rds the size of R580.
I'm not really telling this to you, but if someone wants to talk about that issue seriously, people should really look past the old misconceptions, because Nvidia has been making bigger chips not because of an inherent disadvantage, but because of a reason: compute. Now AMD is going after compute too and their die size is much bigger than you would have expected in the past from a similar performing card in a new process. Nvidia has never really been too far behind AMD in perf/area, but it's just something that needs to be seen with some perspective, and most people just don't.
Take GT200 for example, one of the worst in that respect. It was freaking huge, but it was made in 65 nm instead of in 55nm and the most important thing is that it had 30 double precision processors on top of the 240 single precision ones, that could only be accesed by CUDA (no gaming). DP shaders are at least twice as big as single precision ones, so had Nvidia focused on gaming, GT200 would have been a 300 SP gaming chip. That's a 25% increase! Imagine GTX285 being 25% faster, that's as fast as HD5870 and now compare that to HD4870 and evaluate perf/area again on 55nm (260 vs 480 mm^2). It's a completely different story isn't it?
