In reply to BuzyG:
You should know better than to ask 'why' when fell/hill running idiosyncrasies are involved!
I assume that it's historical and continuity purposes for the Lakes 24h - as mentioned above, some of the 'peaks' would now not make the re-ascent/distance requirements now in place, and it keeps a strong lineage in the record. There was a set of articles in the Fellrunner covering this in recent years.
However, the Munro round has moved around a bit as that's just any Munros starting/ending in the same place - though of course peaks getting demoted/promoted from/to Munro status has added its own idiosyncrasies. iirc, it started in Lochaber, then moved to Kintail, before the last 4 (3 men's, 1 women's) records were set in Cairngorms.
Given Lakes is based on the Bob Graham round, and Monro's has the Charlie Ramsey round in its lineage (please correct me if I'm wrong), there is some divergence in method here, but again I think it's beacuse there's always been a defined list of Munro's (even if this sometimes changes), whereas there's not always been a list of what constitutes a peak in the Lakes. You could do a 'Wainwright's 24h' record, but then this is also to some extent a fairly random list, based mainly on views and not a numerical specification..