The Symbian and WM platforms were essentially developed for 5 year old hardware. It wasn't even until the iPhone came out that everybody started to talk about specs for phones.
Perhaps you didn't pay attention if all you ever owned was a dumbphone, but those of us using WM PDAs and phones for the past decade were very keen on the CPU, GPU, RAM, display and other specs. There were, and are, WM web and print magazines that doted on that kind of information.
From Windows For Devices, to Mobile Tech News, to The Giant Lists at PDAdb ... and many, many more... tech specs have been a huge news item forever.
The chips that will start to come out later this year from the likes of ARM and Nvidia are really the first results of the iPhone influence.
Handheld CPUs and GPUs have been developed and boosted for many, many years before the iPhone was a glint in Jobs' eye.
I can't speak for Symbian from experience but I can with WM. While it may have multi-tasking, the OS at it's core is extremely buggy creating constant issues of stability.
The WM core is Windows CE, which is very stable, and in its latest incarnations, quite powerful. WM Standard (no touchscreen) is stable as well. The problem with WM Touch up until now, is with its limited memory map and 32 process limit. These limitations should disappear with WM7.
MS's biggest problem is that they don't seem to have anyone with a cool consumer vision in charge. When they do show off neat stuff (like Vista widgets under WM), it doesn't come out. (Okay, not quite true for the latter... you can hook up your WM phone to your Vista computer now and the phone will run a single Vista widget of your choice.)
As it is there are six platforms. It is too many. With the ever emerging intergration of the phone, the desktop, the cloud, and the apps they use I wonder which platforms will be around in five years.
Hard to tell. But judging from past handheld history, there'll be even more platforms coming out in the coming years. Everyone thinks they can make a better mousetrap!