This question is more on history than on current issues, but I didn't know what would be a more appropriate place to ask it.
Visa laws in the US are pretty crazy and differ from most other countries. First of all, the validity of visa here is not equivalent to the validity of the visa status. It is typical here for a student to get a visa, which is valid for 1-3 years, and be admitted to a 6 year program, during which it is legal to stay in the US, but a re-entry would require getting a new visa.
Moreover, it is not possible to obtain/change the US visa while staying inside the country, yet it is possible to change the status.
What are the historical roots of this weird system? Has it been like that in other countries as well (and they changed it), or is it a totally US thing?