I disagree. I think Symbian development is a nightmare, and I think that this is evidence that Nokia really doesn't "get it" when it comes to software.
1) How many of those owners of those 300m+ devices have ever paid Handago et. al. for an app? I'm guessing probably something comparable to the number of people using Android right now. That's called 'attachment rate' and it's very low on Symbian, especially compared to iPhone.
2) Symbian Signed. Come on, does it really have to be this hard/expensive? No, it doesn't.
3) Android and IPhone both do web development a lot better than Symbian.
4) Adobe Flash Lite is irrelevant. The only thing Flash is good for is playing back Flash video and Flash Lite can't do that. The rest is "Punch the Monkey" and other banner ads.
5) Symbian Signed.
6) AIKON/UIKON is a f*ing freak-show, and is worse than even Winmo development. I can't count how many stupid ways there are to lose track of resources and system-allocated memory in that mess.
7) Did I mention Symbian Signed?