Just a few lines about a nice post by Marian Schembari on the DBW web site that sums up a few crucial points on the way a publisher may build their own communities. I like in particular this passage:

Since they’ve engaged their community as equals and not marketers, Tor has a foundation in place that enables them to engage fans long before a book’s publication date. This is good for both Tor and for sci-fi/fantasy authors from any publisher, a feat Defendini described as “gratifying”. He also pointed out that the complete lack of “us vs. them” mentality adds to the conversation.

“Publishers need to stop looking at other publishers as competition.” Amen!

I recall when a few years ago I was talking with a publisher about a possible redesign of their website, and (long story short) when I proposed him to link to other sources and external sites he looked at me puzzled and said: “Why should I? I want readers to stay on my site!”.

No, actually not. Not necessarily, at least.
You want readers to recognise you, you want to engage them and you want to create a bond with them.