OK, you need to know a little about how the encoding works for an MPEG IPB datastream.http://www.pinnaclesys.com/files/MainPa ... epaper.pdf
I tried to find a simple explanation but didn't want to spend too much time finding it. Essentially the B frames look at the previous and the next I frame (or P frame) to determine what they are doing. So you can not splice two separate clips together without some form of re-encoding, but the better editors will "smart" encode only the exact number of frames that are needed to get everything back on track. Exactly how you do this in the mentioned editors is something I don't know, but it should be possible with Sony Vegas to do this and output to Blueray or an mp4 files with a minimum of encoding. I know there is a re-sample option in Vegas that needs to be turned off, but I'm not sure about other settings that need to be changed. It may also be a Vegas Pro only feature, I really haven't spent that much time with it.
Now what I can say is that the paid version of VideoPad (or demo version during the demo period) will do this (or so they claim). I have made some edits that required minimal encoding and output into an mp4 file at the same bit rates as the source. They claim Blueray authoring but I never tested it and stopped using it after the demo expired moving on to other choices that currently require everything to be converted on import.