They're using an MP-based system with spells at different levels (and presumably the spells do at least slightly different things), as you can see here:Interesting. At what level do you think the characters would have been in the first episode of the original series? Some of the spells that they pull off seemed much more powerful than standard low level BX fare...
They're also more than made up for by the absurdly generous starting MP, MP per level, and low MP cost of spells. You start with 15-30 MP, gain 1d10 per level, and as an example shield costs 5 MP. So even your worst possible 1st level wizard can cast shield 3x a day. You can also counter magic and sleep cloud up to 3x a day as the worst possible 1st level wizard. And these are the most expensive spells. Everything else is cheaper.Those MP recovery rules are harsh.