The key to the N-Gage relaunch is the connectivity. AFAIK, no other system uses GPRS/EDGE/UMTS/HSDPA, only WiFi. Therefore, the N-Gage will be more connected, and you can download free trials right there on the device, as well as pay for and instantly begin using the full-on game. Also with the higher speeds, multiplayer gaming will be possible, both regular games like Tiger Woods or whatever, but also I could easily see a World Of Worldcraft Mobile, or something very similar. There's no limit to this stuff.
Yeah you may can download demos on the PSP or DS via WiFi, but let's face it, WiFi's not always there, not like cellular data is, anyways. I had the N80 and gave it up because frankly the only place I had WiFi is at my house.
I for one am looking forward to the N-Gage rebirth, but then again, I don't own any other gaming systems other than the venerable PS2 and a Gamecube I recently won at the Work Christmas Party.