A question of dice...

Ok, this is for all of my RPG brothers and sisters. Imagine you have a new game, with a core mechanic that uses a single die-type for all rolls. The question is, does it matter what type of die you use? I know that statistically speaking, based on the manner in which the dice are used, some dice create a greater probability of success.

Here's my quandary. I have a system that I am using that I feel is very universal, and easy to adapt to just about any genre. The problem is, as it stands now, it's pretty much a carbon copy of an existing, published system, that is not open source. So, there may be legal ramifications if I publish a game using it (even if I do so for no profit). I think I have modified it enough to differentiate it from the original system that I started with, but if I used a different die-type, it might completely remove any direct relation.

An additional idea is to use lesser-used dice for it. Right now, I am considering using a d8 or a d12, mainly because these guys get very little love when it comes to the core mechanic. They're usually only used for damage and tertiary rolls like that. The problem I see with doing this is they are only available in game stores. My initial idea was to use d6's, which you can get at any major chain store. But the variation in a d6 is pretty limited. Should this be a concern? Is my audience likely to be anyone who is averse to hitting a game store for a handful of d12's or d8's?