I was however wondering... Is it possible, like with flash/hard drives, that they units are tested prior to being labeled, and perhaps there is variation in the quality of the analog front ends of these scopes. Some work up to 300mhz within some set parameters, others don't perform to the same quality threshold, and they are catagorised as such?
This would make sense when looking at the cost of these scopes. As with most things, making it with tolerance is cheaper, especially if you can rebrand lower quality items as a lower end in the same product range.
This is from a point of view or ignorance on the internals of these scopes, so I have no idea if there are components that have this kind of band of quality, or if its a case of it they work at 300mhz as designed, or not at all?
I don't think that's the answer - since, as far as we've discovered so far, the entire series has always been a single model - although it's possible Rigol has changed something.
As mentioned in my previous post, possible problems with 300MHz could theoretically arise from aliasing caused by a sample rate that's too low. When both channels are on, the max. rate is 1GSa/s - meaning the Nyquist frequency is just 500MHz - and from published BW tests, 500MHz is not attenuated enough by the DS2000 front end. Perhaps this is something that Rigol has tackled in newer DS2302s, although I'm skeptical about it.
EDIT: It just crossed my mind that perhaps there's a new revision of the DS2000A series motherboard because of the recent introduction of the MSO2000A. So maybe some new buyers of the DS series are getting the new revision - which could, in some way, impact the ability to install the 300MHz option.