I don't know where people get this idea that Symbian requires Windows apps. The 5800 has OTA firmware updates and all of its PIM and other stuff can be synced directly through the phone's own internet connection. (That's part of the point of Ovi, to allow on-phone syncing.)
Why is a built-in GPS a con if you haven't even used it? The 5800's GPS is excellent, far far better than the N810s. I've never had a reliable lock with the N810, whereas the 5800 locks every time and quickly too. Also, the 5800 can use a variety of GPS software: Nokia Maps, Google Maps, Garmin etc.
S60 used to have far too little free RAM until about 2007, but from 2008 onwards Nokia got the message and started putting useful amounts of free RAM in their Symbian devices.