то, что

I saw a good link for this question a while back. If someone could just direct me there, I would be very appreciative.

Terrence Wade gives this example:

Она привыкла к тому, что мужчины на неё заглядываются.

Wade only gives the example and does not discuss it. Is the need for "то, что" strictly because the verb demands a prepostion? Is this the only reason to use this construction?

Она привыкла, что мужчины на нее заглядываются
is okay too

you can use it without preposition

If you want to emphasise
She got used to the fact that...,
use то, что

And I think you are right about the verbs that strictly demand a preposition