Well...considering many stalled due to less then expected sales, I would doubt studios would be that interested in taking on the expense and risk of producing complete sets. Lets face it complete series sets at the beginning is much riskier then distributing that expense across multiple series one season at a time. It's sort of like diversifying your investments, if you put all your eggs into one basket and it flops you're in a much deeper heap of trouble then if you spread it around.
There are many benefits to studios releasing complete series packages after individual season sets. For example, all they have to really pay for is new packaging the biggest cost has already been expended in the seasons sets, so this is like gravy to them. The fact that they have all seasons already out means it is a known commodity. With complete series sets they are waiting to get those they missed the first time around and hoping to even entice some to rebuy the whole thing.
Now the "Alley McBeal" release will be interesting since they are attempting to go the other way. A complete series package from the get go to entice the biggest fans, while releasing individual seasons over time to get those not quite sure. I doubt they would have attempted this approach if they weren't fairly confident of the results. After all they have the sales of the other region sets to support their conclusions. It will be interesting to see how this one pans out.