Hey,
I use protools and other music programs all the time. I've always done it on windows but people say Mac's are better. Maybe they are a little nicer since the programs work a TAD differently but I honestly think its a bunch of crap for the most part. If you're intending to use MAC specific software then I think your mind is already made up but if you aren't set on anything specific I'll tell you now Windows has just as many good programs most of which work for both operating systems anyway. The one thing you need to keep in mind is the soundcard/onboard sound the laptop is going to have. That's why everyone generally says get a Macbook since they generally have better sound efficiency compared to a Dell, HP or w/e. I use Protools on the other hand and you need to use an Mbox for it, which has a soundcard in it that will beat the snufs off any laptops capability. Lotta things you need to consider. If you're willing to spend the extra money on the Mac go for it but you'll usually always get more bang for your buck the PC route. I've only talked about sound cards but a decent amount of RAM and a good CPU are important as well!!
P.s. I really have no idea what kind of sound cards you can buy for laptops these days (if any at all), something you might wanna look into or maybe someone on here knows something more but if you could plug one of those into that Asus listed above for example I think your decision would be a no brainer!!
Edit: Apparently PC's can utilize something called ASIO drivers which enables them to mimick the sound effiency of a Mac. That in itself, if true should make your choice a no brainer.