the spuds I used were Sainsbury's taste the difference vivaldis, but I'm sure it shouldn't make any difference

They're ideal for mashing and buttery enough so's you don't need to add butter to your mash or whatever it says on the bumpf

definitely not a salad spud anyways.
I doubt that the spuds would be so important as you think SnS, you can't always get salad spuds and I doubt they'd forgo making the base for the sake of using a common or garden variety of potato. I think the potato is there for texture purposes only as four salad potato-sized king edwards wouldn't soak up a great deal of the 500ml of oil in the base anyway.....
It could be that some people don't add as much water to their base, since the recipe says 2.5 ltr, enough to cover the veg (which may not be at the same level for everyone as it depends on how chunky/fine their chopping is) - or lose more of it in the cooking process, thus the vegetable pulp will hold more of the oil than a more diluted base

I don't use much oil at all when I make a curry normally, yet I always (unless following someone else' method) have the orangey-speckled oil stained plate as I get in the restaurants

I think that's more to do with the way I cook them though
