I have been struggling to add builds into MTM2010 for the past few weeks. There are a few reason why this is a problem.
1) Unable to produce a report on how many test cases were executed in each build.
2) Unable to produce a report on which builds came into test.
3) Unable to log bugs against a build.
4) Unable to produce a report on product quality over a period to evaluate if build quality is improving.
5) Developers are using 3rd party tools to manage builds like CruiseControl.
6) Developers are using a different configuration management tools to manage source code like SVN.
7) Business is using TFS to manage requirements, developers are not due to #5 and #6. Making things difficult to manage for testers.
8) Testing happens on non-Windows platforms like Android, iPhone, Symbian, or other devices like Garmin and TomTom or any other platform for that matter. Coming from #5, #6 and #7.
So there are many reason why this build number is a very important identification item in manufacturing.
I only have VS 2010 Express but the steps are pretty much the same if you use the full feature VS.