File sharing questions

I have a couple of questions that are bugging me and I can't seem to find straight answers anywhere.

First off - homegroups.
Great idea in theory and I found it very easy to set up which is obviously part of the point of it all.
But, how come when I have a file on 'do not share with anyone' a person with another account on the same computer can still access it using the admin password. (I have two computers running windows 7 with two accounts on each)

My second question is:
On 'proper' file sharing both accounts on Desktop can see and access shared files on Laptop yet only one account on the Laptop can access shared files on the Desktop?
The second account comes up with the error along the lines of 'Desktop is not accessible, you may not have rights'

I do have some other questions about this subject but these two are the ones bugging me most!

Bumping as still require help with this and can't find the answers anywhere!