Some will see him as a traitor but he's not really he's just a trophy hunter like most of the top players around. Arsenal over the last few seasons have not been as prominent in the EPL- plus van Persie had a lousy Euro 2012- so accumulatively he's not feeling too good with the situation, despite scoring a bucketful last season.
Wenger hasn't shown that he wants the top players at the Emirates and anyhow the club isn't in too good a shape to attract them.
So he's gone to where the grass is greener, he hopes.
These days the elite players have no real sense of loyalty- they go to clubs where CL football is guaranteed, where the wages are sky high, and where the managers are ambitious. Ferguson is still ambitious I'm sad to say.
The only top player to refuse a big move in recent years was Steven Gerrard, who was tempted to go to Chelsea but wisely decided to stay at a club with real history and glory in the badge, thus truly earning the legendary status.