They are the same machine but I don't think the PrismJet has the drop master tech on board so that would explain part of the price difference. As stated above the Mutoh has a longer warranty and Mutoh requires their dealers to honor the warranty without limitations. The PrisimJet only has a 1 year warranty and, from the looks of it, you only get 90 days of top level tech support. After that you have to pay for support.
Also, this is a completely personal opinion so take it for what it's worth,
Sign Warehouse doesn't exactly have the best reputation when it comes to tech support and as stated above, that is more important than price a lot of the time. Try to find another Mutoh dealer nearby and see what they quote you. It is rare that a Mutoh is sold at full price. You might be surprised what kind of deal you can get.