Where Do They Get Their Information?

I recently started considering a career as an auto mechanic. I have a good degree of mechanical aptitude, far more so than my aptitude for programming, sadly for my current career (it has been so long since I did any real programming I fear how well I would be at it if I was promoted). I did fairly well with lawnmower repairs when I had that for a job, though I had just started getting into that part so only time would have told the full story.
I decided to get a better idea of how much I would make, so I went to Salary.com and used their free Salary Wizard. According to them, Automotive Mechanic I starts at $23,061 (10th percentile) and goes up to $39,586 (90th percentile), with Automotive Mechanic II’s 10th percentile at $30,731 up to the 90th percentile of $49,164. Just for comparison I then ran Computer Operator, my current title, which says the 10th percentile is $22,995 and on up to $40,358 for the 90th percentile… I am not even in the 10th percentile yet. Anyhow, it looks like even at Automotive Mechanic I level (It’s not clear to me if by having an associate degree if I would be able to skip to Automotive Mechanic 2 level or not, or if one has to put a year or two in at the 1 level) the starting income is higher, while the potential is nearly the same. Compare this to what I was considering recently, pilot, where a co-pilot on a turbo prop (where one would likely start on a regional airline) is $21,035 up to $79,609 (compare this to the potential of moving up to Captain on a large jet which goes $80,421 to $129,707). The pilot income potential is much higher, but the first year, if not two years is a killer with very little income, certainly not enough to pay the very high loan back.
Anyhow, I was wondering where they get their information since they say the 10th percentile on a Computer Operator is $22,995 and that is far above what I make… can I be that far below the percentile or is their data off? If their data is off, is it off for all jobs in the area (all the numbers above were based off my zip code) or just some like mine?