I'd say this is true is most cases. In the US, generic drugs only need to be 80% to 125% bio-equivalent (AUC, peak concentration, etc). For most drugs that's fine.

However, there have been a few that have gotten recalled because they weren't bioequivalent. Wellbutrin is a great example. It took the FDA a couple years to finally force the manufacturer to redo the tests and fix the problem.