What they really need is a way to link the demo and full version together in the app store.
Apps with a "demo" version should have a seamless upgrade-to-paid-version experience.
Some apps have done this with via in-app purchases (check out living language for example http://itunes.apple.com/us/app/living-language-spanish-for/i...) which does a great job of this and manages to get $15 out of you by demonstrating the value the app provides very effectively before asking for money.
Apps with a "demo" version should have a seamless upgrade-to-paid-version experience.
Some apps have done this with via in-app purchases (check out living language for example http://itunes.apple.com/us/app/living-language-spanish-for/i...) which does a great job of this and manages to get $15 out of you by demonstrating the value the app provides very effectively before asking for money.