We haven't had a desktop in the house for probably at least 8 or 9 years. I did have desktops in my shop when I had a shop because I got one or two hand-me-downs from work dirt cheap. For the last one I got a Black Friday deal. Those were just basic machines always, mostly used for browsing, music, and very light Sketchup work. All were acquired for a price point, not their specs.

In all my years of computing I've only ever had one machine up and die, an HP laptop that had known motherboard issues. Replacing the motherboard wasn't worth the cost especially since it would likely happen again. Most failures in general have been hard drives (and I'd estimate the failure rate to be similar to desktops) with other random part failures occurring much more rarely. Of the few laptop issues that weren't, I can think of one that got a noisy fan about 4 years in, one that got juice spilled on the keyboard causing sticky keys and one that was a consumer grade machine used for work that developed stress cracks in the housing. The first two were both east at-home fixes. The one with the cracked housing, I bought off work used it a few more years before upgrading, and sold it on Craigslist. In fact the HP is the only laptop that's been in my household that I haven't wiped the drive, reinstalled the OS and sold it on Craigslist for $100-150. For 3 users in my household, we are typically buying a laptop every 1-2 years and rotating who has what. At this point my wife's needs are the most basic so she has the oldest. We just did a rotation and she got one that's 2 years old to replace one that was about 5. She had me buy a new ultrabook and pass my ~1yo ultrabook to our daughter.

The batteries will go bad after a few years and sometimes that can be an issue even if docked full time. Typically you can get a decent aftermarket battery for $50-75. We even get aftermarket at work. That's going to be more of a problem with these ultrabooks which don't have removable batteries but I'd guess there's already a YouTube showing how.

Not having a desktop for us eliminated the need for a dedicated "computer desk" in the core of the house. We have a monitor/keyboard/mouse on a desk in the basement my daughter or I will occasionally use. My wife and I just leave our laptops on the end tables.