I had that same question when I was looking. I did much research and
found that most of the planers are distributed through the WMH tool
group. Jet, Grizzley, ShopCraft, Jet, Delta, Powermatic and many
others. If you do a search on line for the tool manuals you will find
the pictures the same with different part numbers. I found this out by
finding a shopcraft while looking at the Grizzley planers. I called
and talked to someone and he said they were all under the same tool
group. Then I talked to a ShopCraft person and found a little more. I
would not be surprised that even some of the General tools are from the
same distributor. I ended up with a Shopcraft with moveable table 15"
with roller cabinet for $729. One of the local stores was having a
tool sale with reps there and they had a 10% of sale on all tools.

There is a model with spiral cutter head which is more money. I
believe this is also available as a replaceable upgrade on some models.
I have also heard they are from the same factory and with different
casting metal or material. I fnd that hard to believe that there would
be that much difference in cost for the material.
Bill T