I sometimes I get asked this question in many forms and they always make me laugh. The other day I was talking to someone and they were dissing a studio because they used Cubase instead of Protools. I told that person that it really doesn't matter what software you use, it is the person behind the software that is going to make the difference. Personally, I use Digital Performer eventhough I have Protools and Logic as well, DP just works better for me. The sound quality is just the same with most high end software.
So to that end, I would say that you don't HAVE to use Protools to make a great song. Use Protools if you like it but don't make a choice based upon reasoning that says you HAVE to use it.
Do not go by the follow the bandwagon method because "everyone is using it" because in actually they are not. More and more people are using Logic and Digital Performer instead.
Just something to think about!
I am a total music fan and enjoy working in the studio. To know me is to know music.