All part of Jive's efforts to be the Facebook of the cubicle world. It's true that in our case they're pretty meaningless as people rarely use them, but in a corporate setting where most discussions aren't questions and all the users are forced to be regular contributors, the "popularity" of a thread is important, especially when it comes to staff appraisal time!
If for example a discussion announces a new doodad extrusion on the company's Flanged Hoofer, "Likes" would be used just as they are in FB - "I think the extrusion is a good idea but don't have time to say so in longhand". Bookmarks tell the person posting the announcement that a bunch of people are waiting for more news. Showing details of replies isn't important to Jive's target user, as anyone interested in the thread would subscribe to it via their Inbox streams. It's why the Like and Bookmark numbers have popups, but Replies doesn't.
Can the layout of the Details widget be changed? Yes, in theory - with a customization to the software. Will it be? Not likely.