Michelle -- What you count as exercise is up to you. I try to count things that are what I think of as "intentional exercise" -- so in additional to weight lifting and treadmill, I count walking my dogs and doing my back and ab exercises. All of those are intentional and at a certain intensity. Some other walking counts for me -- but only if it registers as "aerobic walking" on my pedometer -- meaning that it lasted at least 10 min and was at a certain pace. So, walking around a downtown area for several hours might net 30-40 min of aerobic walking, but I wouldn't count the time spent shopping in stores or whatnot...
I also count some yardwork, especially if I keep the intensity up. If I work in the yard for an hour, I may count 30-40 min of it, depending on how much I really worked at it... I don't generally count housework, cause I don't do it at enough intensity or duration... and it shows in the cleanliness of my house!
So, we leave it up to you. I would recommend you set some guidelines for yourself. I think it would be great to count housework as exercise... especially if it motivates you to keep moving! But if you start dusting the cat to get in the minutes, it may defeat the purpose!
Also, your criteria may change over time and as your fitness increases!