I agree totally with your posting about the friends not being able to cope with the change and that being the cause of the problem. Although my fiance's wife did not die, they divorced after a 25 year relationship at her request. They had been separated and then divorced for almost 2 years when we met, and he had done his grieving (counseling, etc), but his "friends" seem to be stuck in the past and unable to cope with our relationship.
My fiance and his ex were founding members in a service organization that my fiance is still involved with. Every conversation includes a mention of her and what she is doing now, they have gone to visit her (out of state and a 17 hour drive), but won't drive 10 minutes across town to visit or come to a party we are having. When she is in town, a big get together is planned, so they can visit with her. They are never out and out rude to me, they just ignore me and make no real effort to get to know me. Questions I ask are answered as briefly as possible (if at all) so they can rush back to "remember when". It has even gotten to the point where long time (25 year) friends don't speak to my fiance when we walk in - they have never met me, so it can't be me personally.
We have been together 18 months, and we are happy. Although intellectually I know it is them, not me - yes, it still bothers me.