Why do networks block their shows with graphics?

I've had enough of networks covering half of my TV screen with their logo and now ads for upcoming shows, right in the middle of the picture.

I am watching Body of Evidence on HLN in the lower right hand corner is their logo which is now a 3.5" x 4.5" on my 42" TV screen.  This logo is manila files with HLN in the middle of it.  This logo isn't the usual transparent one but solid so it hides anything of importance that might be on the show.

HLN is hosting the Daytime Emmys this weekend so they have placed a 12.5" x 3.5" advertising the Emmys, 4" off of the left side and about half way up the screen, this is also opaque.  They are covering up about 1/4 of the TV with this crap, while blocking important parts of the show.

Networks wonder why viewers are leaving in droves, this is the reason.  I can watch shows online, which may have 30 to 60 seconds of commercials every 10-15 minutes, less than if it is viewed on TV, and not have the program blocked with this crap.

If I am going to take the time to watch your show, don't make it impossible for me to do so.