Well, mainstreet vegas was pretty influential to make me originally think US players have better bonuses. But after a few posts on the forums other people have told me US players have worse bonus than people elsewhere. I know I'm basing this off hearsay since unfortunately I don't have data. I assume some people who claim either way must have more data than I do? Hope they're willing to share the data.
I do have data (the link to my site is in my profile). I am still refining it but so far out 204 US-friendly casinos I see 203 are offering bonuses to the US players (99.5%). For France the two numbers are 328 and 299 respectively so the percentage is 91%, for Germany 591 and 563 (or 95%), for Poland 506 and 400 (or 79%).
However, you should not be confusing the two different comparisons:
1) US Facing casinos vs. NO-USA casinos : the bonuses in the latter are better, and not just bonuses. That's no doubt
2) US players in US facing casinos vs. Other players in US-facing casinos: here the latter is not superior in terms of bonuses, rather the contrary is true