I personally think this is a very poor move from Hamilton. McLaren are highly likely to fight for the title next season, while it is unlikely Mercedes will. He would have probably had his best chance since 2008, looking at it logically, with such small rule changes.
2014 is a huge gamble and many experts have said whoever gets the best engine could gain over a second, so even if Mercedes has an advantage over McLaren, if Renault or Ferrari make a better engine then they'll likely be slower anyway.
Aerodynamics will still be important and McLaren will get the exact same engine as Mercedes and will likely have more time to spend on making a better car. I would be surprised if Mercedes come out faster than McLaren in 2014.
I'm 90% sure Hamilton would not have moved if it wasn't for his management team, who are just obsessed by making more money at Mercedes. Hamilton often shows that he is easily lead and often does not make his own decisions when it comes to things like race strategy, down force levels, etc. I guess the same has happened here and this time it will likely affect his whole career.
The point maybe he fails to get is that if he isn't winning, which is likely at Mercedes, at least in the short-term, then he isn't going to be as "famous" and thus the sponsors he'll attract will not be the same anyway.
I'm just in a bit of a dilemma now because I have a love/hate relationship with McLaren. I support them, but they frustrate me an awful lot. But I just cannot see myself supporting Mercedes. So I'm likely going to be supporting a driver and then a different constructor.