Earlier quoted context omitted.
Violation of the LGPL? By the author?
Sure, this is possible. However, this author is not violating it. For example, if the regular version were issued with the Pro version merged into it, the author would have to provide an unmodified version in the same distribution lest he violate the LGPL. There isn't much consequence to this, unless he felt the need to sue himself. However, since the author here also owns the rights to both the regular and Pro versi…
Just because he chooses to extend the LGPL to others doesn't mean he is himself bound by its constraints.
In the model you're proposing (where things have one and only one set of copyright terms that apply to everyone), how would things like Libreoffice be offered under multiple licenses simultaneously?