It's certainly a well built camera The body has a full magnesium alloy structure and weather sealing on a par with their professional EOS. It beat the Nikon's D7000 in Mp as it was 18Mp as opposed to the D7000 16.2 Mp. However, the Nikon D7000 has 39 focus points against the Canon's 19. So Nikon have upped the game with 51 focus points and 24 Mp and an upgraded processor on the D7100.
It's unfair to make a comparison between the 7D and D300 as the 7D arrived later. Almost everything in the Nikon 7100 makes it seem like a semi pro dSLR, but in my view all that glitters is not gold. Too much missing for me like AF-ON button, fully sealed body etc. I don't want compromises like dedicating the AE/AF lock to AF-ON!
I think the concern is that if Nikon were to produce a D400 it's liable to be extremely expensive and I'm not sure that the markets there now. I may be totally off target, but that's the way I see things. The semi pro DX market is for serious sport and wildlife photographers. Since I bought my D800 and even with the slow fps, it gives me nearly everything I need for wildlife and does it so well. For extra fps I use my D7000.