The old boys in my club who ride fixed (one of whom rides a fixer older than himself and he's in his 80s) are yer average working class, built things with your hands lot. No ists or ologists to be seen. They seem to do it because where we live you just don't need gears for a club pootle and because they love tinkering with old bikes.
The younger fixers in the club...well, I think that we have one aircon engineer, one doctor or surgeon, and one gentleman archaeologist. The other 'younger' fixed rider that I know and probably the most committed to it is a sociologist.
So, not sure about fixies attracting engineers especially but it does seem to attract more middle class and those who took their education further than in the old days. But this might just be a side effect of the general enlargement of the middle classes and shrinking of the working classes.
Although the other interesting thing in the club, is that only one of the fixed bikes is less than about 20 years old, the ones belonging to the older guys being genuine original vintage fixies, and the ones belonging to us 'younger' ones being converted 1970s road bikes. Only the doctor has a new bike but even that is a converted road bike rather than an off the peg fixed. Not sure what this says about us really, might have something to do with us being a touring rather than racing club?