The cost of maintaining transportation and the unpaid hours from a commute are quite significant. Depending upon their circumstances they could be taking home more money even being paid less.
Here in the UK, just not having to live near London will save you enormous amounts on rent/mortgage as well.
I'm in the office full time (I actually need to be) and I pay 700 a month just in rent on a crappy room not too close to central. That alone is the equivalent of about £17k before tax, and I am a single guy who doesn't mind housemates. No thanks.