To be honest, you also really don't want to look at a laptop for gaming. Mostly the cost, in the long run is just not worth it.
For most people, yes. They are expensive for what they are and the vast majority have a limited shelf life due to upgrade limitations.
But for a smaller percentage of more 'enthusiastic' users, the question of how long constitutes 'a long run' and is it worth trading better performance
now that will last
longer for mediocre performance out of the box?
Admittedly, for what I paid for my laptop I could have bought a Macbook Pro or a high end desktop (current desktop is good enough), but instead I opted for something I needed and that is essentially a portable desktop replacement.
17.3", 8GB, 2 drives+blu-ray and easily upgradeable CPU
and GPU. With a few key upgrades, I could still have this laptop when others are already on to their third. Ultimately spending more money in the long run too may I point out
For me, it suits my needs
now (I'm sitting in a hotel room, listening to music , browsing the web after watching some vids and playing some games at 1920x1080 with high details.) Much more preferable to using some of the laggy "browser/music only" laptops I've used in the past.
However I digress to reiterate that it's not for everyone. Initially expensive and quite heavy/cumbersome to carry around compared to a smaller 15"> 'normal' laptop. Battery life is a paltry ~2hrs with all power savings on. The power pack is also the size of a xbox 360 power pack...
If you have the means, and the need; go for it. otherwise, save the money and buy a good desktop, as mentioned above.
What is constituted as 'long run' is basically the games it will be able to support. Given how things are progressing over time, especially if your desire is to have decent FPS, the thing that cuts into most games will be the Processor, Memory and Graphics card.
While you can still use the laptop for other things, such as videos, basic office use, and web browsing, the cost of the high performance hardware in a small chassis is a bit unnecessarily high IF YOU ARE ON A BUDGET. If you don't care, then it isn't really a problem.
I am more of the 'frugal' type, despite spending the money to get an Alienware computer myself (Mostly cause I wanted to replace my ailing Dell XPS 720 (Which was also a gaming computer) and lacked the time to really research the hardware), I only state that Gaming Laptops are not really worth the worry for long term gaming purposes due to the occasional need to put in a better card.
Gaming computers suffer the same problem, to a degree, although the limitations of monitor support, graphics changes, and expansion of drive space is less of an issue and in the long run, can be easier to deal with due to more user replaceable parts and hardware. You can eek out a bit more use out of a desktop.
As part of another thread I was in, someone wanted to upgrade his laptop graphics card, which is practically not possible. And to be honest, it is also a problem for some desktops as well when you look at integrated hardware some of the cheaper systems will be using, as they forgo things like having PCIe slots (Earlier, they forgoed the AGP slots for integrated video) due to the integrated hardware.
Also, it really depends on what you want to to. A desktop replacement laptop is also great, but I know some people would like to tinker with their system and have more space without having to tack on yet more hardware on. It is just a matter of preference, but again, unless you really need heavy duty computer that you can tote around at a whim, you are sacrificing some things for others, but as far as gaming is concern, you will have about 1 to 2 years of reasonable gaming out of it before the crunch of space and hardware limitations nip at you. (This is coming from a person who still plays Planetside, World of Warcraft, and the random First Person Shooters and watching the disk space requirements shooting up.)