Eccleston wasn't invited to Piper's wedding, whereas Tennant and others were. But then again, how many people invite to their wedding someone with whom they worked for less than a year some time ago? Just because they weren't close doesn't mean they didn't get on.
I believe Eccleston and Barrowman didn't hit it off, according to the latter.
Yea, Weddings aren't something you invite everyone you ever worked with just because you've worked with them. As far as Tennant, there's lots of news indicating they have a close friendship, so, it's natural he'd be invited.
One Day I hope to be the Man my Cat thinks I am
Where are we going? And why are we in this Handbasket?