Is there any justification for that distinction? That is, does Canonical consider the x.10 builds experimental and the x.04 builds stable? I've never heard that.
No, just my personal experience. It's not entirely true for evey release but I find it a good rule if thumb.
IMO it's just better to stick to LTS releases, Canonical tends to make less experimental changes in those releases, because things should work for 3 years. In the other hand, on post LTS releases like 10.10 (which is a x.10 release) they have more freedom to do more under the hood changes.