Thought you might say that. I depends who you ask, but a lot of people say that they wouldn't leave oil in a car for 20,000/2 years without a change. The whole LL service was aimed at lease/company car drivers/fleet managers to
help reduce service costs. I've been told by a few people that it's not ideal and a bit of a swizz.
Admittedly, a petrol car might be less sensitive to it than a diesel. My TDI was on the LL plan when I bought it (ex-co. car) and it appealed to me that it `only` needed a service every 20,000 miles. After some advice, I changed it to 10,000 miles. My driving style didn't suit the LL anyway and I think the car would have changed it to 10,000 anyway (it's meant to work it out by monitoring your oil I think). I change mine every 5,000 miles as the car likes it that way and a lot of other (privately owned) TDI drivers do that.
It's far less of an issue with lease cars because you don't keep the car that long and won't see any detrimental effects during your ownership. You effectively pass any longer term issues on to the next owner. I'm not saying this is gospel but based on previous advice from those in the know.
Service packs can be good value, if you know what you're looking at.