Learn English – Are commas considered superfluous in legal documents

The original sentence is correct.

The appositive which modifies Gu Kulai is the entire phrase "wife of a Chinese politician at the center of a major scandal". You do not need a comma anywhere in that phrase, and it would be incorrect to add one. It is, however, correct to add a comma at the end of the appositive, which is exactly what we see above.

This is so called "legalese". A dialect used only in contracts, law documents and other court and law related sources. Not only it's valid English, it's written in such a way as to not leave any ambiguities, or room for interpretation, using phrases that don't occur in everyday English, but have specific properties of describing places, moments, locations without leaving room for ambiguity. "Whereas", "Herein" or "thereof" are quite uncommon in normal English, but abundant in legalese.

Think of it more like english-as-computer-language, than english usable for speaking; a trained lawyer can understand it fluently but it's very difficult to read for normal people. Ambiguous wording could be challenged in court — arguments about that can drag into months until the opponent drops the case discouraged by the opposite side taking every entry open for interpretation the opposite way it was intended, so lawyers use so called "boilerplates", document patterns used over and over, that were tested in court as leaving no doubts or ambiguities exploitable by opponents, and just fill in the plaintiff names, dates, objects of the cases, and submit that to the court or file away as legally binding contracts.

Answering:

1. Yes, that's used pretty much everywhere. People who use a different language in their legal documents open themselves to irrelevant, lengthy attacks when using these in court — a tactic to wear off the opponent by dragging the case indefinitely becomes viable.

2. As far as I know, "legalese" evolves much slower than mainstream English, so yes, a very similar language was used 100 years ago. Not only that, lots of words that fell out of use of mainstream English still live through legalese, their contemporary counterparts being more ambiguous, or just through tradition.

3. It's correct, though horrible English. Grammar errors are an invitation for discussion "what the author intended", "what the sentence should mean" and as such, avoided at all cost. Still, the style (e.g. repetition, run-on sentences) is completely disregarded in favor of adherence to the "boilerplate".