It's not just about it being offline though although IMO that's a basic requirement for even considering it (and caching a route doesn't count). It's about the UI, clarity and experience as well, and that's where the premium paid for options win. I agree that for many people sat nav is something they only occasionally use so it wouldn't make sense paying for it, but I drive a lot with work and am often going to customers who I have never visited before. I'm more than happy to pay for something that makes that easier.
Having said that, Ovi certainly looks a lot closer to the competition and well worth considering. It'll be interesting to see how quickly they port it, and whether it'll be available on handsets other than Nokia (there's probably an answer to that one out there already lol). The other thing that is a must have with sat nav is multitasking. Shutting your sat nav down to take a call is a bit of a no no lol