David, message replied to.
Re. your question, I've seen slides (of various sizes) in the Moffat Hills most winters so they're certainly not 'rare' but they are definitely 'rarer'.
When the hills here are equally loaded with new snow, avalanches are just as likely to happen (perhaps more so with their broad, flat tops, convex coire rollovers and grassy rather than stony slopes), but altitudes here are that much lower that they don't collect new snow as often, rain/freeze consolidation is more frequent and so are statistically less frequent than in the highlands.
The other factor that makes them seem 'rarer' still is that the hills here don't often see visitors. Many of the Highlands mountains (especially the ones on or near the munro bagger rounds) are people magnets and will have scores of visitors daily throughout the winter. There are tops I could think of in the Southern Uplands that might get just a handful of visitors each winter.
Edited 1 times. Last edit at 09.20hrs Sun 14 Dec 14 by moffatross.