Fruit wise I'm pretty poor really, but I eat a ton of veg. I'm not sure when I started, but I just discovered that there's so much out there that tastes amazing when done in the right combination or with sauces. Yes, a lot of it is cooked (gently), but it's not as nutrient sapping as you might expect. Main problem is things like vit C, which to be honest is quite easy to get from juices as well.
I think the 5-a-day thing is just something that's an obtainable goal for most people - even if 8 would be better, people who weren't used to any fruit/veg would think it was too hard to achieve.