The requested synonyms have been created. It makes sense that asus is the master tag here; they're all just subcategories under that primary tag, so merging made sense.
All questions tagged with asus-pc or asus-laptop have been retagged with asus and the synonyms created.
The thread linked to by Masi to is that of Super User, but also makes sense specifically for Logitech (example provided in there) in which many different products other than computers are made by Logitech. Asus makes computers, and maybe some mobile phones. Perusing through the tag briefly, only Asus computers (Laptops and PC towers) are being asked about here.
Perusing through the Asus tag, and the history of the two tags that were removed, the questions are about Asus PCs or Asus Laptops, which can fall under the same category, while an overwhelming majority of the asus tag covers exactly the same content. Looking at the overlap here, all the Asus questions, including the previously-asus-pc and asus-laptop items fall under asus. While yes, Asus makes motherboards, graphics cards, etc., the majority of questions asked here are about the PC or laptops, and are not about the specific cards or other devices. Unless there's overwhelming evidence these need split up (and I don't see it here), I believe the merge and synonyms are justified.
If the community wishes to reverse this, that's the Community's call, however we had only six questions in asus-laptop and only one in asus-pc, which was the basis of the merge; as well, it appears that only one user was actually using these tags, and only during editing of existing questions to 'create' these tags. Community members were rejecting the tag changes already, which was a further consideration point for the merge and synonym creation.