The DTL bonus tracks ended up on Foundling bonus disc. (See: http://bandweblogs.com/blog/2010/04/16/david-gray-to-re-release-draw-the-line-includes-bonus-material-tracklisting/). The roundhouse material of course was already released on the original DTL bonus disc.
Jitterbug wasn't on Foundling but it was available for free download before DTL came out. Second Halo is an DTL itunes bonus song and afaik it's still on sale there. More to me now is Foundling's itunes exclusive track.
So when the news came out, people weren't too excited about getting this re-release as it only had three new tracks (which we would later find out aren't very good either). A Moment was supposed to be a new single, but you couldn't really buy it anywhere and then DG later said in an interview that the song was just ordered from him and he didn't really care much about it. He hasn't played it live even once. The song was ofc later renamed to A Moment Changes Everything.
Anyway, I don't know why they changed the plans, I remember talk of Foundling starting very soon after that re-release of DTL was going to happen... not sure. Maybe the record company wanted to re-release it and DG thought no way. They messed up by announcing it, though. I have a feeling the same thing is going to happen with the full release of the Lost & Found Dublin gig which was I think promised to come out somewhere (the last I heard DG promised it to be a best of L&F tour instead, it should have come out though already.. ( or the Roundhouse gig (which probably is mostly done but as it's from the greatest hits tour, it's not really that relevant anymore). This is just speculation, though.
As for the UK single disc release. I don't think anyone still knows why they did it like that. It's been talked about so you might wanna search for some threads. Maybe the UK record company wanted to cut on the expenses, who knows! David's core audience has been in the US for years, anyway. It was handled pretty badly though. Heck, they released the two cd version where I live and DG's never even charted here!
You're staring at the sky, but the moon ain't gonna pay our bills.