It may be almost unthinkable in high cost of living areas but it's pretty common for even fairly young people to rent a 2BR and use the spare room as an office/hobby room/etc. I know I did after grad school.

It's another problem with this type of comparison though. What's a "typical" apartment for a young professional to rent in a relatively low cost suburb or small city is likely going to be very different from what the same young professional would rent in Manhattan--even if they're paid more in the latter.