I'm curious if you're referencing dating or long term relationships here (ones that have actually lasted a while.)
Because if this applies to most women, then what's the damned point? get involved only for it to be a matter of time before they lose all interest?
I'm not sure I buy the whole "when feelings change that's a wrap" thing, because if the model you're proposing here is accurate, that is, that their feelings wax and wane (and they do of course), why would you give up the second interest goes down, when it might go back up again at a later point.
Guys get back with their exes all the time, and things get worked out in current relationships, flames get rekindled, etc. No contact for a while seems to do this a lot.
You're basically saying never to try for a girl once interest drops....even in a long term relationship that might've lasted years?