You could easily afford at least a boxter at that price and I don't think a 911 would be too much of a stretch[1]. It really depends on your priorities, though (i.e. do you also want a really nice house/condo, boat, cabin on a lake, etc.) But I would say anyone making $120k/year who wants a Porsche definitely has one. (We are only talking about financial restrictions/opportunities, of course.)
See @simantel stat above. Almost no one earning just $120k / year is driving a Porsche. There's not as much disposable income in a $120k/yr wage as you might think.
Just because not many people making $120k/year aren't driving a Porsche doesn't mean that they can't afford one. In his first question sysk asks if people making that much can afford one. Later, he rephrases the question as, do people making that much drive them. The answer to the second question is no. But I still believe the answer to the first question is yes.
How is it possible for someone to survive okay on $40k/year, but if they earn an additional $80k/year (maybe an extra 40k/year after taxes?) they can't afford a $50k car? As I said, it comes down to priorities. (We're assuming that they don't live in NYC. I don't think it's fair to use that as an example for car affordability.) Even if we assume 80k/year as the baseline, that's about $20k/year extra after taxes. Can you buy a Porsche with cash without saving any money up? No. But if you save for a little bit or get a 3-5 year car loan it's easily affordable. So as I said, I believe that anyone who makes that much and wants a Porsche can easily make it happen.
There's as much disposable income as you're willing to dispose of. I live comfortably on less than 20k a year. If I had a 120k/yr job but otherwise maintained the same lifestyle I could totally drive a Porsche, but my inclination would be to give it away or save it instead.
Few would consider money "disposable" if you had to make sacrifices for it.
@zaroth probably has NYC/SF in mind, where most $120k+ salaries probably are. Pay $40k tax (fed+state+local), at least $30k for rent+utilities, and you're left with $50k for food, clothing, gym, social expenses, travel, and everything else. Out of that, you'll be paying for gas, tolls, insurance, maintenance, and parking. Parking alone will run you $5-10k (unless you're okay with street parking and having that sweet ride scraped up end to end by a truck next week). You could do it, but not because $120k is Porsche-driving income.
[1]MSRP:
911: $85k
Boxter: $52k