okay, back to the plot:
Batterylife:
Any gaming laptop, be it alienware, MSI, Origin, whatever, will have abysmal battery life, and most serious gamers end up teathered anyway. If you need proof, just look at any amazon gaming laptop comments ever.
Upgradability:
Laptops require being broken down, which is a pain for a casual gamer, and if the laptop gets phased out, its parts get harder to find and more pricy because of it. That's just fact.
On the other hand, I could pour 200 every couple of months, and, sans the Mobo or any defects, be able to play most current games at full fps render. Also, the tech sticks, so once I am top, I stay there for a few years longer than the laptop will... So long as I splurge for the clutch mobos, ram, and case right off.
Longevity:
You are lugging a laptop around, and unless you move your desktop all over the place, wear and tear alone are going to be factors (just look at the old hp's that broke at the display hinge so easily... not that I like hp...), so unless you get those uber clean military grade suckers, you may face problems in a year or so.
Also, if something breaks down (hdd on my last one), you're again looking at breaking down the machine, and finding a replacement (thank happysauce that the hdd's are almost universal...).
Gaming:
Let's be objective, when you go seriousgametime, you aren't likely to be moving around much, so, while playing Crysis or something at Starshmuks, may be fun, it's not exactly practical, or even desirable, depending on who you are around.
The plus side of this, lan parties are simply clutch with laptops, and lugging around a pharoah evo (over-exaggeration, I'm sure) from place to place is less than practical in and of itself.
It boils down to what everything ever always boils down to, and that's personal preference. As to the 1ghz thing, yes most have only that, because of the simple fact that laptops are more widely sold as universal work related or simple operation systems, not gaming things.
I don't have a degree in (computerology must be a very specialized class, as CS and CE, or even EE are the only one's I've seen, even up to PhD status) ^that thing, just an opinion backed by experience, if my arguments are lacking, I just need more experience, and as such don't mind being rebuffed.