Pentax, too, though they are really a "digital-only" manufacturer at this stage. In fact, some of their recent primes for their K-series digial cameras have been derided as useless due to extreme AF problems.
People may not realize it but, increasingly, Canon and Nikon do not manufacture their own glass - save for their pro ranges. Pentax no longer manufactures any of its lenses at all (the old "AOCO" factory in Tokyo is rubble).
There's a lot of sharing of components among lens makes now and lens OEMs supply several makes. Thus, it isn't surprising that problems are far-reaching when they occur.