I don't quite understand what you are trying to say. With 16:10 screens, 1920x1200 was a standard resolution. The pixel dimensions for a 16:9 screen of comparable size and resolution are only 1920x1080, which is fewer pixels vertically, not more pixels horizontally.
That 16:10 screens had more pixels than "related" 16:9 screens was an arbitrary decision most likely made for ease of production. Now that that the roles are reversed, with 16:9 being the standard and 16:10 the outlier, it is just as likely that horizontal resolution on a 16:9 model would would be decreased to make a 16:10 screen. Apple has done exactly that with one of their newest models.
A user who wants a particular size of laptop, and who is switching from 16:10 to 16:9, would have to take a model with a shorter screen, not a wider one. Otherwise, they end up with a wider, less portable laptop.
Laptop depth is just as important as width to portability, so there is no advantage to 16:10 here, just selective thinking on your part.