The forum post goes a bit further in explaining the publisher's position, though it doesn't go so far as to explicitly explain the schism. "Steam has adopted a set of restrictive terms of service which limit how developers interact with customers to deliver patches and other downloadable content," the forum post reads. "No other download service has adopted these practices." As with Dragon Age 2, this is in reference to one specific part of Steam's Terms of Service agreement, which forces games to deliver DLC and patches through Steam rather than through a game-specific client. EA claims this to be restrictive, and thus refuses to sell some titles through the service.
It remains unclear why EA -- who, in the past, has offered a variety of games through Steam, regardless of the Terms of Service -- refuses to offer DLC and patches through Steam suddenly, but it certainly appears to be a stance the company is staying firm on. The forum post also notes EA's inclination towards resolving the issue with Valve, saying, "We hope to work out an agreement where Steam can carry Battlefield 3; meanwhile, gamers can pick from the more than 100 digital retailers."