But for the employer it doesn't matter how much the employees spend on their rent, does it?
Absolutely it does for employees who have the skills to be mobile, like software devs. Employers need to pay them enough to attract them to the area and housing costs are definitely part of that equation.
Incidetally, from what I can tell, an average apartment in Irvine is like $2500/mo, an average apartmen in Moscow is under $700/mo.
You're right, but I was speaking relative to what Kickstarter money can give them taking into account the existing salaries they have, while what you're saying is something that would affect the median salary. And apparently the people in gamedev are happy enough to live in California on a $60k salary with a $2,5k/mo rent, otherwise the median salary would have risen.
One further note to add to 29% vs 22% taxes in Russia vs California is that Russian taxes already include the obligatory medical insurance (which is somewhat crappy considering the general level of healthcare in Russia, but still); an ambulance would take you to a hospital for free in all cases, and the (crappy) hospital treatment would also be free for you.