Seconding what JDiver said, it can open up a can of worms relying on anything other than formal, authoritative written guidance from a relevant authority. I understand that TIMATIC is a compiled database one-step removed from the Costa Rican gov't, but it is produced and maintained by IATA, and seems to be considered pretty authoritative.

The point you raise about having "sufficient funds" is a good one... I suppose AA focuses on enforcing the objective regulations, rather than the subjective ones. It would, however, be interesting to see what AA would do if someone showed up with a round-trip ticket but appeared to be penniless.

I'm with you, and don't understand why AA doesn't make the TIMATIC stuff available on their website. In addition to Delta, Continental also provides database access.