Yes, you need to sign-in to the EA account you bought them with at least once for them to activate. Still, having the files on their own makes it easier to use them someday when EA shuts down using either a sunset DRM removal patch or an unofficial method.

Wrong. I bought it retail at release. What I described happened within the first 2 days of the official launch.
I later took the ultimate edition on a steam sale (with which I made the playthrough) and I absolutely CAN'T claim, that the updater was improved - every other startup it failed to launch automatically.

I am. I even payed Bethesda for Horse Armor on their site.
I'm sure I'd love at least half of all ME2 DLCs as much as I enjoyed the game itself. Still, I'll wait for a complete / ultimate / GotY / whatever edition, probably even for a 20 bucks or less sale, before I'd even consider joining Cerberus after the DA:O debacle.
DA:O 2? Never interested me even before the whole "consolisation" debate running over it. ME3? GotY edition or screw yourself John Riccitiello.

I don't get it. You don't worry about EA disappearing for DA:O, but do so far ME2 DLCs?

I hear that sentiment a lot. I wish you luck with the GoTY edition. A ME2 without Shadow Broker seems incomplete.

I don't care about ME2 DLC disappearing*. I care that they're a real PITA to install and verify. DA:O simply let me select what I wanted and then I could go about my business instead of having to track down some obscure web site, individually download 9 files, and then baby sit the install of each one. Hence my description of it as 'clunky'.

*As far as I can tell, DA:O DLC and ME2 DLC are just as volatile.