Fairly simple to put it to you this way, FL Studio is a fairly simple to use program thus a lot of beginners start making music on FL Studio because it's easy to torrent and well, it's simple to use. Plus there is a wealth of online tutorials and knowledge for fruity loops because it is so widely used.
Now, I'll be honest I've heard music made with FL Studio and music made with various other programs and it really all comes down to the quality of the VSTs/Plugins and the Samples you are using, if you use any at all.
I've heard amazing stuff come from people who use FL Studio and I've heard equally amazing music from people who use Pro Tools.
If you are not using a microphone and don't care about Pro Tools plugins then really any DAW will do. However, if you are recording vocals or live instruments, drums etc. Pro Tools is great and the plugins available make it that much more attractive to the music professional.
I personally started with FL Studio about 5 years ago, moved on to Logic, then to Reason 4...
Now I use Reason 5 and Pro Tools religiously because what I do requires the use of high quality plugins and vsts/samplers etc. Plus recording a lot of vocals requires a powerful Daw, and I love Pro Tools simply because of the vast library of Plugins available from numerous manufacturers.
Don't be afraid to change your DAW as you progress, FL Studio is great but it does have limitations (pros and cons) just like all other Daws.
I recommend Reason 5 for productions and Pro Tools for Vocals and/or Live Recording to create samples or actually live record a whole composition. If you eventually get into the Studio world and participate in recording pop/rock/ or hip-hop you will find that Pro Tools is found at every major studio and is used by virtually every major studio for recording live instruments and vocals. That is no opinion, that is a fact, anyone who is telling you otherwise has not worked within a major studio or has anti Pro Tools sentiment because they have yet to learn how to use it for themselves, and they will usually complain that the Pro Tools DAW is too complicated.
Hope this helps,