Wait, what? The only official statement I know stated that it's been "about 200 years". That is quite enough for that much vegetation to grow, for well preserved metal structures to start falling apart, and such.
We shouldn't really read too much into a simple joke. ^_^
If I remember correctly (and I'm not saying I do, mind you), VALVe originally stated, back when the first information was being released, that it was set some 800 years in the future. Now obviously that isn't the case, but I still have a hard time imagining that all that still could still be there in 273 years. Especially all the wood and stuff that's in the lower parts of the enrichment center.
Anyway, I should probably get some sleep as I may not be thinking entirely straight right now. -_-