When something is worth 25% of the mark, say, what parent in their right mind is not going to seize hold of it and give it a good going over?
Of course, just because a parent has given it a good going over doesn't mean it'll be better for the experience.
There's an interesting set of assumptions about parental help. At GCSE there's huge amounts of pearl clutching over take-home work, parents getting involved, etc. The concern is that some large proportion of parents can provide guidance on a GCSE history (say) assessment which will improve it over the child's unaided work, hence the need to move continuous assessment to exam-condition (yeah, right) CAs. In MN land, it might be true that all parents can read and make helpful comments about a history submission; for a lot of kids, it won't be.
But the same concern isn't present for A Level, where take-home coursework is still a large part of some history (in particular) syllabuses and the EPQ is nothing but. It's as though there's an assumption that the only people with post-16 qualifications are the teachers. We read and commented on drafts, and provided some technical help on referencing and so on; nothing that a teacher wouldn't do, but available on tap rather than once a week. A large portion of children won't have effective parental help in constructing an A Level assessment, but for those that do, it will be extremely useful.