That is, once you pass the 75% then all non-standard version X blocks get rejected, that means that those small percentage of miners have to keep getting 5% of the blocks hashed and also that they have to be hashing them to a version < X (because if they were hashing to a non-standard version X, they'd be getting rejected by most miners because of the 75% threshold having been passed). I apologize if I misunderstood something.
The 75% rule means that new version blocks are verified. Once 75% is hit, then version 3 blocks (or higher) that fail the new rules are rejected.
It means that the 75% threshold doesn't really mean much, since you can still include the transactions in version 2 blocks.
I think a better rule would be that after 75% is achieved, then version 2 blocks would have to meet the rules for version 3 blocks. After 75% is achieved, then version 2 blocks are votes to reject the BIP.
Clients could have a rule that if 75% of the last 1000 blocks are greater than CURRENT_VERSION, then the client produces coinbase only blocks.
95% becomes the point of no return. All blocks must be version 3. Old clients could continue making coinbase only blocks and hope for the best.