That list is heavily populated with Fort William to Mallaig services, are they "specials" or a regular bit like Paignton - Kingswear?
Paignton-Kingswear is a heritage railway, where I believe the track is privately owned and speeds are limited to 20 or 25mph (correct me if I'm wrong). Fort William to Mallaig is a Network Rail route that is still part of the national network, with three ScotRail diesel services per day if I recall correctly. I believe the speeds aren't necessarily subject to that 20/25mph limit and all locomotives used have to be 'mainline certified' etc. Again, correct me if I'm wrong.
A regular steam service has run between Fort William and Mallaig for many years during the high season, but I think it counts as a charter service for which seperate tickets must be booked (I don't think a standard National Rail return ticket would be valid on the steam service). Years ago there was also a similar regular steam service on the Cambrian Coast Line between Machynlleth and Porthmadog/Pwllheli but was withdrawn when (in 2011 I think) the line was switched over to
ETCS▸ signalling.