It's totally unfair to blame Owen. He is a world class player who we have to hold on to if success of some sort is to be achieved in the near future. All strikers go through bad patches, not helped when the team generally goes through a bad patch too.
I would say one of the main problems goals wise, is that we rely almost totally on him to score the goals. That's fine, it was the same with Rushie. But then again, you need 2, 3 or 4 others to wade in with 10+ goals a season (particularly the striker's partner) to back the main striker. We don't have that.
As for penalty takers, it seems to be the norm these days for the main striker to take them. No doubt to get the goals to game ratio up, and to try to win the top goalscorer accolades (Van Nistelrooy scored 12 Prem penalties in winning last season's Golden Boot! With a total of 25 goals I think). It's fine if they can put them in the net, but you need somebody with confidence taking them. At the moment, you'd go with Gerrard who is playing his heart out. If Owen is taken off penalties, surely that will knock his confidence further.