Realistically, many on the lots can be a bit outdated (even in the same year) so they get discounted a bit more I would think. Check the build date on the left front sticker.
We were looking at 2013s originally, and some on the lots had build dates dating back to as early as 05/2012 but showing as 2013, which explained to us why some had this shade, some had that, some had this TV, some had that, Some had these chairs, some had that, etc. The RV industry doesn't follow a model year change schedule, they pretty much phase in changes whenever they want based on new design, existing inventory of parts, etc, so two units built in the same month can be vastly different. For instance I just saw a 2014 with the new basic outside solid brown colors, but the old front and rear fiberglass clip (the one without the LED lights). Nothing wrong with the dated ones on the lot at all, but just know what you are buying.
Another thing is the Dealer typically does not order his inventory units with tons of hidden options such as disk brakes, heat pumps, etc because it makes the price higher than what the competitors are showing. Again, if it has everything you want, there is nothing wrong with the inventory units and the price should be better on the inventory unit because of build date and lot expense.
We have ordered the last few, and its fun. Pick all the stuff you want (I didn't say need

) and see what comes up. You should be able to negotiate a substantial discount off MSRP. If you want to check yourself, try several dealers and shop on the internet. Typically the large discount units are closer to the actual price.
You can expect some custom work - but like ordering a burger without pickles at McDonalds, it can kick your order to the back of the line making delivery a bit longer when they are busy. Ours was grabbed from some early ones in production and was completed within 4 weeks, but as a consequence, some of the little "favors" we asked for didn't happen such as changing the bedroom décor and a factory dryer vent.
Hope that helps, Enjoy shopping!