Well, some art I see a lot, others I don't. I only buy OSR these days, really (occasional Traveller)
For instance, you constantly see the Outland Arts/ William McAusland stuff. Even Kevin Crawford uses them. But it's because it's pretty nice work for a really good deal. Like what, $8 for 20-30 pieces a pack?
Similarly, you see a fair amount of the Purple Duck stock art (especially that rat picture). I use a lot of it myself. Again, because it's cheap ($3-4 each and often on sale for much less) and high quality for the most part.
But a lot of start art you don't see a lot. Because some of it's more expensive and some of it really sucks. There's a certain old school artist that can't draw hands, for instance. Yet he charges a lot. No thanks.
If you are paying 1/3 of original art, you must be using the higher priced stuff that is rarely seen.