Without a way for end-users to actually make judgements about application efficiency, there will never be any real pressure to make efficient, native apps.
I'd say it's more of a "without a way for end-users to compare" --- the average user has no idea how much computing resources are necessary, so if they see their email client taking 15 seconds to load an email and using several GB of RAM, they won't know any better; unless they have also used a different client that would do it instantly and use only a few MB of RAM.
Users complain all the time when apps are slow, and I think that's the best point of comparison.