I think its down to wear & tear or fashion really and of course your income. We seem to do ours every 3-5 years, not necessarily carpet(bedrooms only)and like kbaby do touch ups, but its our own hard work and we enjoy it , when its finished. And kitchens and bathrooms can get makeovers too not just new ones. Invest in washable paint, wish I had found it earlier.
I think it is totally personal. My parents have lived in the same house for 40 years, and I think each room has probably been painted two, perhaps three times (apart from the full redecoration when they moved in as the house had been rented out for a few years before that). Mostly my mother chooses pretty much the same colours too. They have done the kitchen twice (new units, tiles etc) but the bathrooms still have I think the fittings put in after the war (the house was bombed and restored then).
My FIL on the other hand seems to redecorate every two or three years, and it's not just a lick of paint either.
We probably fall in between, we did the bathroom and kitchen in our first house once (when we could afford it!), made no change in our second house until we moved out and the tenants wrecked it, and can't afford to upgrade the kitchen in our new house (because all our money got spent on the repairs). I'd hope that a full redecoration would last for ten years really, with perhaps a lick of paint after five.