@Jeffro - It's a single line to copy and paste. Nothing can go wrong. Most users that will want to disable this will be the ones who know about their database. Most users set their database up and forget about it, without caring how big it gets. Only those who have some knowledge of WordPress will care about it at all.

On the other hand, look at it from an interface perspective: more options in the UI creates more clutter. Having an option for every single thing in the options would expand them greatly, at little to no benefit. There are tonnes of hidden options available at the moment which most users don't know about, because they don't need them.

In case you're wondering about whether clutter in the options matters, take a look at this wonderful essay by Joel Spolsky.