1. You can request a follow-up visit by a supervisor to confirm that you do not have line of sight for getting the DISH installed. Tell them you are going to get the mega pack and HD equipment and they "should" be falling over themselves to get somebody over.
2. One of my colleagues has Dishworld and while quality is ok obviously the satellite route is much better as you will ALWAYS get the best possible picture (other than weather events which are rare).
Search on Google for DishPointer site and use that site to see if you have line of sight by selecting 118 satellite and your address. Also, there are other options to install the dish - on the ground, on the side of the house, or even on the roof to bypass any obstructions. Dish should be able to do this. Talk to them.