Your link goes to a comparison between 3 Dell Mini 1012 netbooks.
The first one is a pretty typical modern netbook. 1GB RAM, Win 7 Starter, 250GB hard drive, low-end N WiFi.
The middle one adds "cellular" Internet and GPS builtin.
The top one is missing the N card (G only), but it adds the Broadcom video decoder card. Also, I think all 1012 netbooks with the Broadcom card come with a higher resolution screen, too (1366x768). If I'm right, the 1024x600 screen listed is incorrect.
As for performance, most netbooks can play 480p videos encoded with the h.264/AVC codec well (typical "HQ" web videos). HD videos won't work as well. Due to poor programming, Adobe Flash (videos in webpages) struggles more than most video playback software. The Broadcom card should enable HD video decoding, even in Flash.
While I'm on the topic of Flash, Firefox addons to block Flash help alot on netbooks (NoScript, Adblock, etc). Running a whole bunch of Flash ads, games, etc., in separate tabs can cripple a fast computer. A netbook has no chance. When you need to run a Flash game or app, it's easy to allow just that one.
As for where to buy, I like to buy refurbs from Dell's Outlet. But even on new computers, you can sometimes find great deals at Dell. I think it's harder to find a great deal on a Dell elsewhere, but if you do, buy it!
I think most current Dell netbooks are just variations of the 1012. If it says 1012, then no matter where you buy it, you're getting the same basic machine. The differences are limited to options, like WiFi card, screen res, cellular Internet card, video decoder card, etc.