There really is no difference except for having the dealer nearby for classes, repairs, etc. If you are an experienced sewist, you probably wouldn't need lessons on a machine as simple as the Janome Jem; I would imagine the manual is enough. If you clean your machine well and don't allow lint to build up, it shouldn't need yearly maintenance. (My Bernina 1230 has not been in the shop for at least 12 years and is probably due for a good cleaning and going-over by a technician.....)
Does the Janome Jem have adjustable stitch length and stitch width? That is one thing I always want in a sewing machine because it makes machine applique easier for me.
If I were buying a Janome Jem, I would purchase it from Amazon (especially since I have Prime!). With Amazon, it is very easy to return a machine if you don't like it or something is wrong with it. (This is easiest if it is listed as sold by Amazon, I think, but probably also works for 3rd party sellers. Check policies if you are unsure.) Read *all* the reviews of a machine on Amazon before purchasing, no matter where you purchase; these often provide useful information. Here is a link to Janome Jem machines on Amazon:
http://www.amazon.com/s/ref=nb_sb_no...s=janome%20jem
p.s. Most dealerships will not allow you to return a machine once you carry it out of the store (even if never taken out of a box). They will, however, take it back if you decide to upgrade to a more expensive machine. There are some exceptions, but you'd better be sure of the particular dealership's policies (in writing if possible; verbal assurances by sales people can be unreliable).