Having just returned from Nepal last week, my understanding talking to locals and reading the local papers is that the authorities want to stop people trekking without a guide, ie/ solo, supposedly to prevent missing trekkers- their words not mine. Nothing to do with porters or porter ratios. In other words solo or in a group, you'll need a guide. Not sure where Cbee heard about a 1: 1 ratio- sounds improbable not to mention unworkable.
From what I heard the Khumbu Valley area operators are ignoring this directive, not that I went there this time. Not sure if the directive as yet actually has any teeth to be enforceable.
As I went to a restricted area it has long been mandated that a minimum of 2 trekkers plus a guide to gain entry in these restricted areas. Didn't bother me, the guide was very handy knowing the current state of play regarding landslips and rockfall areas. Interestingly, even though we were in a "guide only" area there were still a handful of signs for missing ( presumed dead!) western trekkers at some of the tea houses- good reminder to tip the guide well!!