Was only a matter of time. A super-smart move for Comixology and one that made the initial investors very happy. I personally just don't see Marvel or DC staying with (IE: Paying for) Comixology to carry their books. I think they will revert to all in house before too much longer. Smart move to sell now, before that even gets a chance of gaining traction.
And for going Kindle ... keep in mind that they do not have access to Google play (or of course Apple) so be sure you are okay with that before buying a Fire

I just use my Kindle as a reader (as that is all it is

) but hear of people that were pissed thinking getting a Amazon/kindle tablet was going to be like getting an Ipad or a Google one like Samsung's Galaxy or Google's Nexus.