The reason for that (I think) is not that the 5110 is less robust, but that the 3210 and 3310 were much more widespread - they came onto the market when mobile phones really started to become widespread, while the 5110 (their predecessor), with its stub antenna and bulkier size, looks a bit like the last representative of the previous era...
A month or two later you could get the 3210 for free, plus a better contract from orange, that took advantage of the MMS options - plus had the programmable ringtones which was soooooo much cooler than the 5110.
I was lucky to jump from the 5110 to the 8210, and then to a 8250 which I adored and used on an off through to 2007 - when I moved to the E61 then e71 - which both still hold a very special place in my heart!
MMS is much later technology where the user data go over HTTP, which implies at least WAP support and GPRS to be really practical.
With stats like that, it is no wonder that Nokia leadership thought they had cell phones figured out and ended up completely oblivious to the challenge the iPhone presented.
Was a joy to use the joystick hehe