It's not to do with the fact that it reaches 90 degrees, but H&S don't like the procedure for if it was to get stuck at 90 degrees, hence why it will now only reach 70.
No idea, but if the towers one still reaches 90 I'm guessing it's due to Thorpe having a different model and therefore the procedure for it getting stuck at 90 degrees would be different.
Should've been more clear in my first post, but it's not to do with the fact its '70% safe' but the procedure for if it was to get stuck at 90 degrees. If the ride could no longer reach 90 degrees due to its performance I'm pretty sure they would just get rid of the thing.