Seems the lifetime of the battery is on a par with that of the hard disk, which on many laptops is not officially a user-serviceable part. (And which, ahem, is typically warranted for a year at most.) But plenty of users replace their non-user-serviceable hard disks when they eventually fail, so I expect many Apple laptop users will do the same with their battery.
The thing is: we’ve had two trusty Powerbooks overhauled completely by Apple recently for a flat fee of $318 each. That included batteries, hard disks, and in the case of one unit, a display, among other things, and the units were returned fully refreshed, down to new little rubber feet on the bottom. $318 to make a five-year-old product like-new is far from unreasonable. So, even though many folks will replace their non-user-replaceable batteries themselves, the alternative that has you so worked up is far from the end of the world.
I’ve never voided my warranty on my Compaq notebook through either Compaq or Microsoft for having had 4 different hard drives in my laptop over the past 2 years as well as 6 or 7 different iterations of XP, Vista, and Win 7 or Linux versions. I don’t buy the idea the hard drive is a non user serviceable part. Heck Microsoft has an 800# specifically for when you upgrade a major component like a hard drive and need to re-register your Microsoft product. On the part of Compaq I had to low level format my original 80 gig Seagate hard drive when I returned it to Compaq. I don’t trust anyone having my data at all.
I guess $318 to refurbish your 5 year old Powerbook, but I see it as $318 can pay for 90% of my next PC laptop with the first released version of Windows 7.