But the black one has friction ridges that are a tiny fraction of a millimetre. Little enough that for constructions where friction doesn't matter (you just want to connect two parts and something else will prevent rotation), they are mostly interchangeable, but the grey ones work better to connect wheels that you actually want to be able to spin, and the black one works better if you want to build a rigid structure.
You don't tend to find two parts that similar with that kind of minor difference for most non-lego plastic building blocks because most of them don't manufacture their parts precisely enough for it to work.
[1] https://www.bricklink.com/v2/catalog/catalogitem.page?P=2780...
[2] https://www.bricklink.com/v2/catalog/catalogitem.page?P=3673...
The patent expired long ago, but few companies will put that much effort into making those shapes that precisely.
https://www.youtube.com/watch?time_continue=1&v=Tnb-LUM0yd4
edit: Ah! He did it for this stack exchange question - https://bricks.stackexchange.com/questions/1754/how-much-usa...
Legos are amazing.
Whenever someone goes out of their way to complain about the profit someone makes (as though its dirty somehow) I always wonder... have you ever calculated your own profit margin? Having a job is rarely free and, unless you you're just living off prior earnings/trust fund/etc. this is a figure you can come up with. Most people I've known, including myself over time (I've for worked everything from minimum wage to very healthy salaries), have done pretty well in the profit margin percentage area as compared to the 32.8% markup you cite.
To be fair, you certainly didn't register a complaint per se in your comment, but something to think about before making that complaint.
Maybe don't be so judgemental for no reason?
(I just explained why Lego is expensive. Nothing else.)