Software patents tend to be uncreative, uninsightful bits of legal sophistry used by large corporations and patent trolls to suppress competition and extract legal fees.

Most software patent infringements result not from seeing the technology in use elsewhere, but pure secondary derivation independent of the first. This alone calls into question pretty much any violated software patent, and because it is so easy to violate such patents no searches are -ever- conducted.

On top of that, patents last 20 years from date of filing which in the software world is an eternity. Patents issued in 1990 would only be expiring this year, and we've moved way, way beyond where we were in 1990.