Ok we all know that the 2.0 adds AVC formated video compatability and the web browser right? So the 2.1 firmware doesn't flash these things to the firmware right? Just 2.0 If they put all the updates into a new update 10.0 firmware could be up to a 1gb file! So I strongly recommend you all save every single firmware on your computer because if you have 1.5 and upgrade to 2.1 the webbrowser shall forever be gone to you since you can't upgrade to firmwares before the latest one.
What I'm saying in shorter terms is if you have 1.5 and upgrade to 2.1 the 2.1 upgrade will not come with the browser and avc format so save all the eboots on your computer and upgrade one at a time so you can have all the features (except upgrades that have new security *cough*2.1*cough*).