Jeff Kaplan of Blizzard has just announced, in the December 7th Overwatch Developer Update, embedded below, that maps and characters will always be patched in as free updates. This is particularly interesting because the game is often viewed as Team Fortress 2 being distilled through a DOTA 2 filter. Those games offer purchases of specific weapons or heroes (Update December 8th @6:15pm ET: I meant League of Legends when I was talking about hero purchasing — I changed it to DOTA 2 for Valve symmetry, but they apparently don't sell heroes), respectively, which would be an easy way to monetize the title. The problem is that it could lead to a situation where a team doesn't have the necessary tools to counter a strategy that the opponent is fielding, not because of in-game logistics, but because the players didn't buy some piece of content ahead-of-time.
Note that, while I haven't played the game, I've been hearing that weapon loadouts for individual heros will not be a part of the game, free or otherwise. A chosen hero will be the same across all players. I say this because Blizzard hasn't denied the potential for weapons or loadouts as DLC, but that seems to be because they're not even considering them at all.
Beyond heroes, maps will also be patched in for free. This is likely for a different purpose, of course. Heroes make a huge impact on the balancing of a game and the list of available strategies. The decision to release maps for free is likely to prevent parties from being split up because individual members don't have all the required content. StarCraft II approached this issue by allowing all members of a party to be upgraded to the highest-level member until the group is disbanded. For a game like Overwatch though, which seems likely to have more than two or three tiers of content, segmenting off a handful of maps unless you play with friends is probably too petty to monetize. Might as well just give it to everyone and charge once at the door.
Here is TotalBiscuit's thoughts on this issue and others, from before this announcement.
The beta for Overwatch will be shut down on December 10th for the holidays. It is expected to reopen in January. I'm guessing that they have an update planned, but they don't want to push it until after the holidays for support reasons. Thus, rather than leave an old build open for a month, where people begin to judge its already-fixed quirks with holiday binge-gaming, they decided to just pull it. They might as well let anticipation build, and welcome back users with something new after the holidays. This is just speculation, though.