Just a small point. asus-pc and asus-laptop mean the same thing (PC == Personal Computer, a Laptop is this too), if we are going to debate this, should we not use asus-desktop rather than asus-pc?
That first point also demonstrates my concerns with splitting the asus tag, where does it end?
If we split asus in to laptop and desktop versions, what about servers or ultrabooks or tablets or phones or tablet / laptop hybrid, if we split it once, we would have to split it further down the line, when questions are asked that those, very specific, tags do not cover.
While I am not for just removing the brand tags, I can admit that from a question answering perspective, they are not the most useful tags to begin with and adding desktop tells us nothing more that the brand tag did, we still need to know the exact model of the desktop.
To summarize, keep it simple, asus as a tag has value for people looking for asus related issues, whether we add a desktop or a laptop, these people still need to check the question and splitting the tags only causes confusion for the new users viewing them in the long run.
We should also merge zenbook and any other modal specific tags in to asus.
Here we only are discussing asus but what about the other brands? We will have to separate them out too, it will be chaos.