There are many "7"s in FFVII, I did a thread on this a while ago. Certain things took "Seven Days" to happen, and the are seven characters in your team, if Vincent and Yuffie aren't included (they are optional), there is also a pub called Seventh Heaven and it is in sector Seven, also most characters have Seven Limits (3x2+1).

I think they called FFVII FFVII, because they realized how stupid it sounds, and most people had already begun calling each FF what it was originally called (i.e. FFIV was FFIV, not FFII) - at least at my school they did.