As Apple rolled out other models of Mac laptop and desktop systems, SSD's became a Build-To-Order option in select models, often at a stiff premium. Many Do-It-Yourselfer's opted to perform an SSD upgrade themselves after the purchase. With the majority of SSD's in the 2.5" laptop drive format - most were drop-in replacements in MacBook and Mac mini systems. A fewfull-size 3.5" Solid-State drives arrived, many used disk adapter brackets and cases in Macintosh Pro towers and iMac models.
In the years since - SSD storage has made mind-blowing performance improvements. Drive capacity increased at ever more affordable prices and performance doubled - then quadrupled as rapidly evolving SSD controller chipsets and Firmware advanced.
It's the increased density of the flash NAND chips that's pointing towards the future. The latest MacBook Air models with custom SSD module are pointing to a future where our notion of a 'hard drive' doesn't necessarily have to occupy the paperback size space of a 3.5" drive, or a laptop disk's deck-of-cards form factor. To deliver ever more compact and lightweight mobile computers - our current notions of traditional spinning platter drives and their physical bulk is likely to end sooner than you think.
As with the new MacBook Air's, an off-the-shelf retail SSD drive upgrade or replacement limits options as Apple implements a proprietary mini SSD card in a different form-factor. OWC is the sole manufacturer who offers higher-capacity (and somewhat more expensive) MacBook Air SSD card upgrades as an alternative for these new Mac laptop models.
And these prices are inconsistent: Depending on exactly which Mac and which model - Build-To-Order at the Apple Store charges as little as $300 to choose a 128GB SSD to as much as $825 to add a 256GB flash drive. On higher-end Macs, Apple has more leeway in margins to alter prices on a per-Mac basis. On lower-end models, the cost of the SSD is higher. On higher end models the same size SSD option is priced lower. Go figure.
For some, the peace of mind, and value right out of the box may make that included SSD option worth it. It's easy to say Apple's solid-state storage upgrade prices are anywhere from high to outright outrageous. But when time is money - and given how dramatically faster SSD drives can make your Mac - a flash drive option may pay for itself... in no time flat
For Model-Specific DIY Upgrade Info - See:
MacBook SSD DIY | Intel Mini SSD DIY | 3.5" Pro and iMac SSD DIY
Apple tends to have little middle ground: Sometimes they opt for end-user serviceable parts and easy access designs - and at other times (Such as in the Aluminum iMacs or Mac mini) require painstaking procedures. Recently -- as with the Uni-Body Apple MacBook + MacBook Pro family - and Pro Towers -- even Apple is finding their support and service infrastructure benefits from easy to access hard drives. And such designs make their customers slightly happier about long-term ownership.