I've done them, just to prove to myself that I could, but I didn't enjoy them.
I'm not fast enough to complete a century in 4-5 hours. Four to five hours is about my limit for any activity--work, sleep, traveling, visiting people, whatever. Cycling is no different for me.
Last century I did, I arrived home completely bored, antsy, and upset. Didn't want to even look at the bike for two days. Did a nice metric today with the club. Just under four hours. I arrived home a happy man, looking forward to tomorrow's ride, and Sunday's too.
So ride what you want to ride. Me? I'll stick with 50-70 milers, thanks.
Despite having ridden many, many 100-milers, I have a lot of sympathy for this view. Once I'd done it a couple of times, the idea of riding 100 miles just to get into three figures rapidly lost its appeal. I really don't understand the guys who, after a 95-mile ride, carry on for five more just to do the hundred. Who cares?
But I don't entirely agree about the 4 - 5 hour thing. On a tour, or sometimes just when out for a day on the bike, there are days when just riding (not necessarily continuously, there is always the option of stopping at a decent pub) is the only possible option. 100, 120, 130 miles, who cares? There's just a wonderfully meditative, Zen-like quality of being on the bike and at one with one's environment. That's how most of my long days have happened, anyway.