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Although that is the modern way to match the original sash pattern and the glazing bars themselves can't cause a problem with the double glazed unit, the frame still can, and it's the lower part of the window where most of the water that runs down the glass collects which always rots first. There are well known best practices for bedding in and sealing double glazed units in wood, and the trade is improving because it's more popular but lack of a proper maintenance schedule will lead to them rotting and can lead to the double glazed unit being damaged. Then the whole DG (sorry but it gets boring typing double glazed all the time) unit needs to be replaced which involves disturbing all the beading then properly sealing them again. Unlike a normal pane of glass where the putty hardens and drops out, worst case scenario the glass has to come out, normally it's just a repair to the glazing bar, re-putty and paint again.
Having said all this I made a back door for my own place in hardwood with double glazing. I left a 5mm gap around the dg unit using plastic blocks and sealed the beading inside and out with an appropriate sealant. I'll also be able to keep an eye on the paintwork, especially on the beading. It's also easier with doors because access is generally easy.
There are new types of dg unit arriving at normal glass outlets which can be thinner than the old standard 4/6/4 which should allow more direct replacement sashes to be made. However you still have to counterbalance the weight. Having given the subject a lot of thought I am still recommending weatherstripping and insulated curtains to my clients.
Airhead-
I have double glazed sash windows, with some fancy coating and gas filled. They used the original wooden frames so you can't even tell they are double glazed (my building is semi protected because it's some sort of poor-mans-listed). Think they are around 10 years old now and no issues, I can try and dig the companies details up... although I have a feeling they were pretty expensive (I live in permanent fear of breaking one), the previous owner quite proudly mentioned the company was on Grand Designs.
chrisbmx116
Can you not design this out by using plant on muntins / glazing bars like Mumford & Wood sash windows, for example? Granted they don't look exactly the same as a trad sash window but I think most people would be hard pushed to tell the difference.