This is because the buses have to be able to be fitted with guide wheels, and the B8s can be fitted with guide wheels.
Exactly! These are the only Stagecoach examples and for that reason.
AFAIK, Arriva have had none save for a long term demo, First don't have any, Go Ahead don't have any save for some inherited with EYMS and don't think NatEx's bus ops have. So I find it hard to believe that most of the bus industry is wrong whilst Lothian, TrentBarton and Delaine are the ones getting it right
The fact is that First obviously did specify Volvos for many years, whether that be B7TLs/B9TLs or B10BLEs/B7RLEs. However, since 2012, they have received very few and notably, some of the last B7RLEs in 2012/3 were for the South Hants Eclipse services and have since been replaced by e200mmcs. The reason for this is that Volvos, in comparison with e200mmc and Streetlites, are heavy on fuel - that is the major saving not the oil in gearbox and engine changes. If you're burning an extra 50 litres of fuel a day, it equates to an extra £15k a year or so. That is why the industry has gone for lighter, more fuel efficient vehicles and First have recorded e200mmc on urban work returning over 9mpg - much better than a heavyweight vehicle.
Whilst you can buy some parts "off the shelf", most of those heavy duty components are inherently more expensive and, as is being experienced now with ageing B7RLEs, major unit failure IS costing a small fortune.
Don't get me wrong - I much prefer a B7RLE than a Streetlite max or even an e200mmc but there's a reason why the industry has changed.