jatlh SuStel:

-wI' has the effect of nominalizing the verb into the subject of that verb. A vutwI' is the thing that performs vut, the subject of vut.

If you were to say *vutlu'wI', you'd be trying to nominalize the verb into a nonexistent subject. No one in particular performs vutlu', so it makes no sense to talk about the noun that performs vutlu'.

As I said, I'd like to hear what MO has to say on the subject. It's bound to be more nuanced, not to mention a lot less bombastic and opinionated. Perhaps his explanation would also shed light on Klingon concepts of grammar and why a verb plus {-lu'} takes the prefixes it does.

Why are we dropping the h in gh?

'Iv maHqoqvam? 'ej Hoch ghItlhHa'ghach DabuSmeH poH Daghaj'a'?

~mIp'av