Yes I have seen a few DAS systems and often been the one asked to come in and figure out why they are not working as good as the design engineer said they should. I've also been on the receiving end of 'you setup the AP's wrong for the DAS and that's why its not working properly so you come and fix it now for free'.
My experience with these type of systems is that its a great concept that really doesn't pan out in the real world and yes I totally agree with your observation that it just seems to be a whole lot of expensive cable. One client I worked with who deployed it was told that it will save them a lot of money buying AP's to install the system and in the end it turned out to be just as expensive so really they didn't save anything. My opinion still is that to deploy a VoWLAN properly needs a good wireless engineer who knows how to take into account the tuning of the system they are working with to make sure that the phones have a low latency, high signal connection and that the area's they are used in have excellent coverage. DAS or no DAS, the engineer still needs to know how to tune the system!