I believe Disney may have put some effort in masking the length of the single line to address this issue. Might be something that grocers could learn.
A couple factors, though, would seem to undermine grocers' incentives to change their queuing approach:
One is the need to maximize inventory on the sales floor. They would need to do a lot of reconfiguration to handle the single line. And that might potentially reduce floor space for stock.
The other issue is that grocery stores fill a core human need: food. We're going there regardless of the line configuration.
I'll bet some grocer out there could make a name for themselves by shaking up the traditional ways we shop. This queuing idea is one example. Would be a smart move in fairly commoditized industry..