Some people are in properties (mainly new builds) where there is *only* FTTP. And so the lower tiers exist to cater to those who can't afford the higher speeds - I think the 40/10 tier was £25pm from BT. If you're in one of those I think the checker will offer the lower tiers in the spot where it would offer FTTC if that was available. Or it may be you have to ring them up to ask for them.
OR's tiers were previously 40/80/160/330, now they're 55/110/220/550, and BT have been rebranding their versions of them. I'm not sure why - possibly to align with FTTC at the lower end, or because they were more conservative to begin with?
I'm not sure what happens if you have both FTTP and FTTC. But I expect that's relatively rare (somebody did a FTTP on demand, perhaps)
Theo