It's become an inevitability in the electronics works: whenever a device is released, a smaller, most cost-effective version is in development.  Such is the way with handheld video game systems; from Nintendo's Game Boy to Sony's PlayStation Vita, our toys have been shrinking and reworking features for decades. Over at USgamer, Jeremy Parish has turned a review of the new model of Vita into a brief retrospective of handheld redesigns.  It's interesting stuff and a fun recap if you're joining the industry late.  Here's a look at how the Atari Lynx emerged from its R&D cocoon:

The first-ever handheld hardware revision is one of the few flawless victories, though it shouldn't have been necessary in the first place. Atari streamlined the utterly enormous Lynx into a smaller form factor. This didn't affect any internal features like hardware power or battery life, but it did make the system portable, a trait severely lacking in the device's massive original release. In truth, the initial concept for the Lynx was more in line with the Lynx II's design, but based on focus testing Atari came to the conclusion that what people really want from a portable console is a system so large you need a backpack to lug it around. Remember, kids, focus testing kills.

I tend to buy once and stick with my choice.  I happily ran a lot of miles out of my original Game Boy, Nintendo DS, PlayStation Portable, and now 3DS and Vita.  Had any of them become completely inoperable, I'd have replaced them with the latest and greatest, but why do that when the ones I already own work just fine (well, my 1989-era Game Boy is suffering from digital glaucoma, but the used Game Boy Advance SP I picked up some years ago (admittedly a revision, but it's my first purchase in the GBA line) handles my GB needs just fine).  Besides, modern redesigns lose great features.  The DS ditched its second cartridge slot needed for GBA play and secondary DS peripherals starting with the DSi, both the PSP and Vita have tinkered with lesser quality screens, and even the GBA itself lost a headphone jack when it became the otherwise better SP model.  There's always a trade-off, so I figure why not do my best to stick with the developer's original vision and intent?  Nobody wants a compromised experience (well, except for the Nintendo 2DS owners, anyway, but that's the whole point of that device and it does have a place out there).