7 years does sound about right. My dad's got a client that moves every two years! good business, but still. This is the beaty of buying an existing (or as you may say, "used") home. It's been upgraded somehow by previous owners, and you get to inherit the improvements w/o paying for them in full! I.E. a backyard pool, cheapest is about $20k. Once the seller sells the house, the pool only adds about $5k to the value of the house! You add your own improvements.
I.E. My current home. It came upgraded with finished garage, piped in music throughout house (even garage!), hardwood flooring in the first floor, flourescent lighting in garage, central vac, gas stove, upgraded chandaliers, artificial grass in the back, under the stairs storage (previous owner did it) crown mouldings, and a keypad style lock on front door of house. What we've added here so far are : laminate floorings in the second floor, tile flooring in the bathrooms, granite countertops, repainted whole inside, added chair rails throughout ground floor, built in plasma tv, new garage door opener.
Besides not all new homes are the best. I've seen homes that are only 2 years old, and you'd think it was 20 years old by the way they took care of it, and homes like a 30 year old home that's been upgraded and taken cared of and looks like it's only 10 years old!