The guide was on 101 only when there was SD, and they did not have the problems of so many satellites. With all the HD sats, they had to stack sat signals together, but there was not enough frequency band room to put all the sats on the same cables. The stack plan for HD is:
101 signals come on the same cable(s) as 99
103, 110 and 119 signals come on the same cables.
If you look at a DirecTV multiswitch (WB68/616 or SWM8/16) you will see the inputs marked with these sat designations.
That means when you are tuned to a 103 channel, there are no 101 signals on the cables from the dish, so no 101 guide. DirecTV duplicated the guide data on 119 so when you were tuned to a 103, 110 or 119 channel, you got guide data.
When DirecTV decided to build a 3-LNB Slimline LNB, they were faced with a problem. They could not really change the stack plan because there are millions of receivers out there using the signals the way they were. So somebody came up with the clever idea of making the 3 LNB slimline take the 101 guide data and put it on the cables with the 103 signals, so the receiver would think it was coming from 119 even though there were no 119 signals.
When the SWM system came along, the sats are not stacked any more to the receiver, the SWM system gets the correct transponders and puts them in the eight available SWM slots (that's why the limit of eight tuners). The guide data has its own SWM channel and the data always comes from 101.
But that's why you can't just tell a receiver it is connected to a (non-SWM) 3LNB dish when the dish is really 5 LNB. On a 103 channel, the receiver is still expecting the guide data from 119 on the same cables as 103, and it's not there. A real 3LNB, or an SWM system, solves that.