In all of my gas powered guns they all shoot all of their ammo before running out of gas. I think moreso the problem is that you can't buy high cap mags for gas powered guns which makes sense because gas powered guns are meant to be as realistic as possible so for instance the M4 GBBR can only fit 30 rounds into it just like the real thing.
Gas guns are more realistic and aimed more at the collector than the gamer however that's just what I've found.

One of the MAJOR bonuses to gas guns is the trigger responsiveness. When you hit that trigger, it shoots, unlike electric where there is trigger lag before shooting. You can get an AEG upgraded with devices that will help them have less trigger lag but I've never met (but have only been playing a couple of months) an AEG that was as responsive as a gas gun.

I just bought two m11's and really like to dual wield them and have been using them more than electric over the last couple of weeks. Although, shooting at 30bbs per sec even with a 50 round mag I need 8 mags to play a full game with.

Again, to each his own.
There are surely advantages and disadvantages to each, what really matters is to get something that works for YOU. When you get your gun all sighted in and set up perfectly for yourself, there's nothing like it!