I wouldn't worry about it, as Avid will provide excellent support for it.
There are probably well over 100,000 Mach3 users, and anyone that's used both will tell you that Mach4 is much better.
Mach4 was based on Fanuc code, so you shouldn't have any issues with it.
And keep in mind that WinCNC is about $2000-$3000, depending on options. Mach4 is $200, plus another $200 for the ESS that Avid uses with it. So that's part of the price difference between the Camaster and AvidCNC.