I am Chinese, and I grew up speaking and reading both systems, so my knowledge wasn't from an INTRO BOOK.
You need to look at the history of the language itself. Mandarin was only used in a very small area back in the days, its originated form Beijing. Your example of Hokkien is not correct, Hokkien is a modified form of a dialect known as "Fukien", which is from the "Fukien" province of China, and you should ask your wife again, the "Hokkien" should be what is commonly known as Minnan. Its still only a dialect. In school, the type of "Cantonese" that people are taught (Writing and reading) share the same grammar, structure and meaning as their "Mandarin" counter part. Any Chinese character thats used in Cantonese and not in Mandarin are considered Slang.
The written system is not call Mandarin, there is no such thing as written Mandarin, its Simplified Chinese. The reason why they call it Simplified Chinese because it was modified from the original "Traditional" Chinese, this was done within the last 100 years (Since 1956ish to be exact), they were once written the same way.
Ok, I accept your argument that I was using just one or 2 character as an example, I didn't say I was correct either, everyone is just posting base on their opinion, myself as well. As I said, I grew up speaking both Cantonese , Mandarin, and some very limited Japanese. And base on my limited knowledge of Japanese, I just find it closer to Cantonese
EDIT: Have a look at these 3 wiki sites:
Mandarin Chinese - Wikipedia, the free encyclopedia
Just read the first 2 paragraphs....
Simplified Chinese characters - Wikipedia, the free encyclopedia
Read the introduction.
Chinese language - Wikipedia, the free encyclopedia
3rd paragraph:
Standard Chinese (Putonghua / Guoyu / Huayu) is a standardized form of spoken Chinese, based on the
Beijing dialect of Mandarin Chinese , referred to as 官话/官話 Guānhuà or 北方话/北方話 Běifānghuà in Chinese. Standard Chinese is the official language of the People's Republic of China (PRC) and the Republic of China (ROC, also known as Taiwan),