I agree that it's extremely frustrating, and likely a large part of WP's problem. I understand that a lack of powerful OEMs is a problem, but Microsoft is powerful and certainly capable of throwing around money. If they really want to WP to be a success it's a pretty straightforward path.
1)Have a low-end phone, maybe 2 mid-range phones, and a flagship phone.
2)Announce these phones within a reasonably short amount of time of their release (while they're still on peoples' radar)
3)Do whatever is necessary to ensure that these phones are available on all the major carriers
4)Market the hell out of them
It seems so straightforward, I really don't understand why they keep half-assing it with long lead times, carrier exclusives, and missing products (the 830 is NOT a flagship at all!)