We output it because historically Reflector was unable to recreate the original source constructs. However this has obviously changed over the past few years, for example, with the support for lambda expressions, F# (obviously still alpha), and now iterator blocks, and so there's increasingly less need to output the compiler generated code.
However, I think it's not as simple as merely turning off its output, as it can provide useful information where Reflector was unable to recreate the original source construct. A better solution would, I think, be to keep track of which blocks we have (and have not) been able to recreate source for, and then remove only those for which source constructs have been successfully generated.
Unfortunately I can't give you a timescale for when this might happen because we have other priorities for the v7 release. Obviously we do intend to improve this but I can't say more than that at the moment.