Right..............
Basically, satellite signals are transmitted between 10 and 12GHz. When they get to the dish, they are down converted into a signal at around 1GHz by the LNB (low noise block downconvertor). This is done to allow the use of normal cables between the dish and your box. Without going into boring details of how this works, the box has to tell the LNB how to down convert. This means that you need a LNB per tuner for everything to work well.
There are 4 options when downconverting, low/high band and horizontal/vertical polarisation. In normal household installations, you have a LNB that is capable of downconverting 1, 2 or 4 (I think they do 8 as well) signals and you have a run of cable to the dish for each LNB. In a flat distribution system, what happens is a different LNB, called a quattro LNB, is used which has 4 LNBs, one each for high/low/H/V. These signals are then fed into a multi-switch which takes those 4 signals and allows them to appear as if they come from a dedicated LNB for each feed.
Yes, I am a geek. Yes, I have a quattro/multi-switch installation here. Yes, it was the first one the installer had ever put in a house rather than a hotel