This may seem a bit late, I know, but I still haven't come across a good reason for the UI change in the XB1 version of the beta. In the 360 version, selecting one of your online friends from your in-game friends list brought up a set of options including Join fireteam, Invite to fireteam, etc. In the XB1 version, the Join fireteam choice was gone. The small icon on the person's nameplate still showed when he/she was joinable, but there was no in-game way to actually accomplish this.

It wasn't until my third time playing the beta on the XB1 that I finally found that you could join them by leaving the game, launching the XB1 friends app, finding your friend, and finally selecting the generic Join game option.
(I also read after the beta that the Join game option would be available anytime you brought up your friend's Gamercard.)

So, the obvious question: why was the simple in-game method to join friends removed from the XB1 version of the beta? Was this a logical Bungie decision, and I'm just overlooking the obvious? Or is Microsoft trying to push their system utility apps by requiring developers to use them for this sort of functionality?

I'm guessing it is Microsoft. At least the View Gamercard -> Join Game path was only a few extra clicks and didn't require going through the cumbersome Apps.

Ease of use trumps garbage any day. Hopefully that gets fixed somehow.

... MS added several organizational options to your Friend Lists?

I.E. Destiny FL. Destiny Raid FL. Destiny Crucible FL and etc

Time will tell. I'm not a big fan of the Xbox One's annoying and out of touch UI as it is. Its ease of use compared to the 360 is a joke. Any improvements to what currently exists would be wonderful. And if Bungie can make it easier in-game by allowing me to bypass a lot of what the Xbox One wants me to do, then even better.

Time will tell. I'm not a big fan of the Xbox One's annoying and out of touch UI as it is. Its ease of use compared to the 360 is a joke. Any improvements to what currently exists would be wonderful. And if Bungie can make it easier in-game by allowing me to bypass a lot of what the Xbox One wants me to do, then even better.

I haven't had the XB1 long, but its UI seems so much less intuitive and functional than the 360's. Great, I've got picture-in-picture, but I've lost voice message and file system management capabilities....

I don't know that Microsoft is behind the joining game issue, but there wasn't any obvious reason that I could see for Bungie to remove functionality that was clearly already built. We'll see what happens down the road, but I sure hope Microsoft would encourage rather than force developers to integrate their games with the system apps.

The XB1 software just isn't polished yet, and a one-size-fits-all model rarely turns out well. Plus, I would prefer to trust developers to continue to fix and support their own game's functionality rather than rely on Microsoft to do so.

I've only played multiplayer on one game on XBone (Forza 5) but from what I've seen, this appears to be normal. Game invites seem to be handled entirely through the console UI. There's no invite option in Forza 5, it's just done through the friends menu. I'm not sure if this is a requirement they force devs to follow, or if there's some technical thing that keeps it this way.

When the XBone first launched there was no distinction between XBL party and game party. To get in a Forza 5 session with someone, you both just had to be playing the game, and form an XBL party. I think MS believed this was easier for users to understand, but it was also hugely inflexible. Later they updated the system to separate party invites and game invites more, but there's still signs of the old system (Forza 5 still behaves very similarly to how it did at launch, and there is still no in-game invite mechanism).

Up until now it actually didn't occur to me that this might be the case going forward on that platform. I just assumed Forza 5 stayed how it was because they couldn't/wouldn't change the game that much after launch. But maybe that's just how XBone is going to roll for everything? Or, maybe it was just Beta weirdness. I dunno.

This is correct. For some reason MS wants you to view the other player's gamercard in order to select the option to join them.