They do care, but they're also developing software pretty quickly and they break stuff just like everyone else. Only, when they break, people tend to notice, and those people tend to spread word around pretty quickly.
When I worked at a hosting company, we'd have at least 5 shared hosting servers (with ~75-200 websites on each) go down each day, and yet we had a reputation for good uptime, because comparatively, we DID have good uptime.
I think the problem is that most people think about uptime wrong. Uptime is a compromise; a trade-off. You can pay for more uptime with diminishing returns after about 98%. Running one dedicated server colo'd with decent fault recovery systems in a decent datacenter will probably get you 100% uptime most of the time, until it doesn't, thus ~98%.
If you're going to attempt to get beyond power failures, you'll need a second server (or "instance") somewhere. If you need the capacity anyway, this might not double your costs, but you may still have unused headroom. You could buy flexible computing power by using shared hosting ("the cloud") or whatever, but it's the same problem.
Once you get into a state where you have a global business, customer demands, supplier issues, vendor lock-in, etc, it becomes a numbers game. You can hire (more|better|famous) devs and possibly get more uptime. You can test more (and slow down feature releases) to get better uptime. You can break stuff (and pay for the recovery + lost face + downtime) to decrease downtime. Everything is a trade-off, and right now it makes sense to chase about "four nines" of uptime -- 99.99%.
Four nines is 4.32 minutes per month -- four minutes and nineteen seconds AT MOST once a month. This is very possible for many large services and while it does have cost overhead, it's manageable.
TL;DR don't go chasing waterfalls (100% uptime.) It's not practical. It may be possible, but it depends on how long. 100% uptime for 10 years would be a pretty damn lofty goal. In my opinion, it's much more important to recover quickly and gracefully with awesome communication with your customers than it is to be up 100% of the time. 100% uptime goes unnoticed, but consistently great customer service does not.
