30 years ago .com may have been intended specifically for commercial purposes but that is buried underneath three decades of use as a generic catch-all TLD and as such using it communicates almost nothing about the site in question.
.org is by convention and usage largely reserved for nonprofit organizations. As such use of .org (intentionally or otherwise) communicates that the website in question is for a nonprofit.
xxx is, at merely 4 years old, brand spanking new. There hasn't been time for intent and practice to diverge meaningfully, ergo it's perfectly reasonable to assume a site that uses the .xxx tld is in fact a porn site.
