I've had the same PC desktop for over eight years. More accurately, the same beige, boxy, bland enclosure. Nearly every component, including the motherboard, has been replaced at least once in order to meet or exceed the system requirements of a new video game.
Soon I'll have to entirely replace my desktop because, I'm told, the ugly late '90s enclosure isn't compatible with today's motherboards. It will be an end to an era but I'll always be able to recall with miserly delight all the money I saved only buying the components necessary to play the latest games. It wasn't easy. I look at desktop advertisements the way children look at puppies in pet shop windows. I close my eyes and image how fun and fulfilling my life would be if I could bring just one of them home with me.
Buying a desktop ala carte has gotten easier over the years. Only in recent years could a manufacturer direct PC be purchased without a keyboard and CRT monitor bundle. We're not out of the woods yet. Despite being able to configure a laptop in over a dozen ways there are little to no options for upgrading those components and forget about user-replaceable components aside from memory (and removable media bays.)
It's about upgradability. The more a device can grow with you, the economical it will be in the long run. So buy what you need now and save money. Then just buy upgrades like memory as it's needed. So ask the notebook salespeople at you retailer for models that provided upgradeability. And if the manufacturer arbitrarily changes its standards so that new components aren't compatible with your old laptop that you specifically picked to endure obsolescence then don't worry; that's normal.
I have found that many Compaq Presarios will be equipped with less memory than they can handle making them both inexpensive and upgradeable.