There seems to be 2 popular sizes for panel makers to go with in the under 52" range.
Some companies like 40" and 46" panels. (Samsung is one company that makes these sizes)
Some companies like 42" and 47" panels. (LG.Philips is one company that makes these sizes)
It really just depends on who is making the panels for each TV and what each one costs compared to the TV they plan to make. For instance, not every Samsung TV actually uses a Samsung panel, but it makes sense that all of them are 40 and 46 now since that is the sizes they make and they can swap their panels with other companies depending on supply.