Parabolic reflector and Feeds
A dish has a radiating area of approximately that of a circle. That area being \$\frac{\pi D^2}{4}\$ = 0.785 sq metres for a diameter of 1 metre. 

If the feed point is 10% the diameter of the dish then it will obscure an area of 0.00785 sq metres i.e. one-hundredth of the dish area.

So if 100 watts are being projected by the dish approximately 1 watt is wasted by the area of the feedpoint. That is a small price to pay even if that power were totally lost (and that isn't always the case).