It certainly isn't a huge deal, it's just that I don't understand why they do it. If you have a 44" printer it is nice to have that extra space for nice borders, especially on say a 40x60 inch print you can have 2" boarders on each side for either matting or if using magnets to display. You have a nice looking border to do that with. It looks a lot nicer than 1" borders on each side.
There is something to this 42" size though because Breathing Color makes their canvas in both 42" an 44" widths. But if all these printers using this media are 44" it just seems odd to me to have to buy a roll 2" shorter than that capability. And yes I make all my test prints 8.5x11 which comes out perfectly on the 44" width.
I don't understand the 42" either. But do you really need the extra 2"? I mean, I don't think I print over 40". I guess it all depends what you're doing though.