Why are there so many cross-over episodes of One Piece and Toriko? I've noticed that there has been many cross-over episodes involving One Piece and Toriko.

In fact, Toriko's first episode has One Piece characters in it.

Is there any kind of connection between both of the two series?
Some possible reasons:


The manga each is based on are run in the same magazine.
The anime are aired on the same TV channel in Japan on the same day.
The anime are made by the same company.


Sources:
anime info: http://www.mahou.org/Showtime/?o=ET 
manga info: http://en.wikipedia.org/wiki/Weekly_Shounen_Jump#Series