Actually R2 got memory wiped too, all droids got frequent memory wipes, but Princes Leia inserted a disc/something (plus her message to him) which contained mission details, That's why R2 knew about Obi-Wan and Luke divulged his approximate location. C3PO however was elsewhere at the time, and so didn't get the mission, he just thought R2 was acting up.
r2 didnt get his memory wipped it was just "protical droids mind wiped". r2 never had his mind wiped since leaving naboo. and konobi owned r4 not r2