$FOO in php is cheap.
$('FOO') in jquery is expensive.
I don't think using $ to signify "Run some load of jquery code" was a wise choice. Newcomers who don't know what is going on under the hood will regularly write loops with $('FOO') inside them, which is crappy code.
They're doing what they think is best, so I don't blame them. I blame jquery for making it look cheap.
Why on Earth you assume that someone starting to use jQuery will come from PHP background, and more over, why should that person think that $FOO in PHP is cheap?
I guess anyone thinking in terms of performance cost will be smart enough to understand what $() does in jQuery, especially when advice to cache selectors is on every wall.
They're doing what they think is best, so I don't blame them. I blame jquery for making it look cheap.