Keep in mind LG has been having sync issues for years. There are several threads on newer models that have it, and I have a 32LC7D(about 4 years old) that has it as well.
As for having different processors. It all depends on how they make the TVs. More often then not with these budget TVs you will have things like cheaper tuners, bezels and speakers. It makes more sense to buy the decent components in bulk from major manufacturers then to get low grade stuff and continually replace them when they fail.
I don't know how all of these companies work, but I just bought an Emerson 42" plasma because it was cheaper then the bigger names and knew it was just a rebranded samsung(only reason I bought it). After going into the service menu it appears to just be a PN42B430. I can actually change it to a 5 series, or a lower number 4 like any other sansung can. The tuner and everything is reported as the same stuff in my returned LN46B530. The service menu is exactly the same as any recent Samsung TV.
I would always discount 2nd tier brands, but if you do your research beforehand, you may find yourself with a set of equal quality to the bigger brands(which are problematic as well). It's possible Vizio uses the cheapest crap available to sell a TV, but I don't think they are any worse then LG in terms of PQ and reliability.
Haha, sorry for the rant there..