Haven't heard about it, but I suspect it's the minima in class D airspace in a control zone? A can give a few considerations to reducing it in the control zone at least.
From the perspective that no separation between normal VFR and IFR is provided, hence it's see and avoid, it'll bring up some issues.
When you provide traffic information to a VFR, and he stays the required distance from clouds, it'll give both the IFR and VFR ample time to aquire each other then the IFR comes dumping out of the clouds... if the VFR can linger around right below the clouds, that option is removed.
Hence when you get closer to the clouds, by requesting special VFR, ATC will make sure you're separated from other special VFR and IFR flights.
With todays requirements of transponders, it may not be as necessary, since an IFR flight are able to "see" a VFR flight before dumping onto him. And further you could argue that keeping VFR flights from the path of inbound and outbound IFR flights should be sufficient. Furthermore that ATC has an obligation to "avoid collision" between aircraft, so eventhough no separation is required, we may end up in a sticky situation, with the lawyers, if aircrafts collide after being only given traffic information and nothing else.