Wine made from grapes, we drink on Pesach.
Brandy made from grapes, we don't drink on Pesach.
What's the logic?
Aside from
@moko's answer, you can't really ask "what's the logic?" about Pesach minhagim. I mean, you can, but you aren't likely to get a logical answer for the most part.
I could be way off base, but the way I see it is that "Lubavitch minhagim" for Pesach run on the baseline is we don't eat anything. We only eat that which we have a mesorah that we *do* eat. But obviously that is an extremely tough standard to live by and so accommodations were made over the years, leading to new things being added to "the mesorah". My father doesn't have sugar (even boiled) nor dairy, but he allowed it in the house. So some kids have grown up and still eat the dairy and sugar they grew up with, others took on those stringencies as adults well.
I know many who were extremely strict who have loosened up as they saw how their kids were reacting to the stringencies. They'd much rather their kids be at home celebrating Pesach with avocados than not having avocados and having their kids running away at the earliest opportunity. I can already hear some folks screaming "how hard is it to do without avocados for a week?" But sometimes it really isn't' the avocado and what it symbolizes. You have to be smart about it.
