"Is it the administrator of the network who runs these bots, like chanserv at their disgression for security reasons? (that maybe why i'm confused. I thought it was a characteristic of IRC/MIRC.)"Nope

- IRC is simply the chat protocol itself, the foundation bricks for getting to chat with people worldwide. mIRC is the viewing screen that makes IRC make sense! You can't have one without the other you might say. Neither however come with any sort of administrative "bot" or service. They are loaded on to the network/server and if the bot or service uses mIRC to do this then it's within their rights to do so. This is unlikely however. IRC services are generally programs unto themselves and are part of the IRCd, they do not have their own client. As for bots, they might not necessary be using mIRC.
"In any case I appreciate the points of view.. however I still think yahoo is incorrect managing their channels in this way. just my opinion."Welp, I'm afraid there's not much we can do about that - Yahoo!, like any other IRC service, sets their own rules. Channels can kick you out for any reason they like, server IRCops can have you disconnected for any reason, including no reason.
This page may be of interest.
That said, I highly doubt Yahoo! *want* to drive users away, that's simply madness and they don't benefit from it. Perhaps you should search around and find a way to contact Yahoo!, preferably a department that is related to the chat feature, and see what exactly is going on

Happy chattin' & G'luck!
Regards,