I saw this happening too. It turns out that having more than 1 roku device on an account shares the channels so channel adds/deletes on one device changes the others. i resolved this by setup a roku account for each device.
Ironically I love the fact that I only have to add a channel once for all of my Roku devices (3 of them), instead of having to add the channel to each device separately which takes a lot more effort.
I am sure that is why it was designed this way since most users don't want to go through the hassle of adding channels to each device and trying to remember which channels they liked and added to one of their other Roku's so they can then add them to another one.
I guess I could see 2 possible reasons (the second one is a big stretch though) for the multi account approach:
1. If you have a Roku that only you use and your significant other or kids have another Roku that only they use and you each don't want to see each others channels that you are not interested in.
2. If you have one of the Roku units literally locked away / hidden in a room to hide it from your significant other and don't want them to know you added the bikini channel (just an example).
The 3rd would be IF it offered parental control (PC) you could ensure the kids don't have access to movie channels (given they do have titles with explicit scenes and nudity on some of the movie channels), but it does not offer PC at this time.
I am personally glad Roku designed it this way.
Microsoft Windows should offer a similar option out of the box - 'network software installation' for all PC's in a household. E.g. this could be performed on a per program basis (a checkbox e.g. that indicates you would like to install this program on all your computers simultaneously).