The "best digital camera" is the one you can afford. That said unless you're a true enthusiast spending £3-5k on a top end body it's pretty pointless, might as well go for something along with the 70D or d7100/7200.
I think it's a given that anyone asking about cameras that high end is spending that kind of money.
I brought it to HN from a different angle. Most photographers crop and downsample to help them establish proof of copyright (since they don't have negatives). With 4K screens becoming commonplace, it seems like they're about to lose that arms race.
But even then most DSLRs are at least 20MP+ giving enough wiggle room to crop/manipulate the image and still have a high enough resolution to display on 4K devices.
I don't think it will be an issue for a good while yet and by that time I'm sure new bodies will come out to take advantage of it.
I think the parent was talking about currently available models. The D90 quoted is from 2008, and nowadays even good compact/superzoom cameras can do useful 4k photos.
I brought it to HN from a different angle. Most photographers crop and downsample to help them establish proof of copyright (since they don't have negatives). With 4K screens becoming commonplace, it seems like they're about to lose that arms race.