Shamrock you are right, but it has to be remembered that an island of 2400 and a smaller tourist industry than the other islands cannot economically support Dash 7s and 8s - the load factors just wouldn't work.
They struggle to fill the Trislanders at times (especially in winter) and the only time of year a Dash 8 would be nice would be at Alderney Week when the Trislanders have to do about 12 rotations a day from Southampton
. However, the Dash 8-100 would need a few 100 metres more but I'm sure you could squeeze it in in an emergency.
With regards to failing mainland air links (on the part of Blue Islands), they could have done some advertising in the Brighton area - I never recall seeing any anywhere in Sussex! This would have got them many more passengers and possibly made the route sustainable. With regards to Bournemouth, I believe there was a little more to this than met the eye as they pulled the plug on Guernsey - Bournemouth as well. Shame really.