Old sections and new sections of a site

[smo]

I have developed two sections in my site long back and now they are doing well. One is my article section ( in article directory ) and other in my sql tutorial ( sql_tutorial directory ). Now both sections are doing well and any time I am adding a page to my sql section then within a week I am getting visitors from google. So I am adding one or two articles in my sql section in a week and traffic is increasing accordingly.

Now I tried to add one more section exclusively on PHP ( php_tutorial directory name ) and added some content. But found that they are not doing well in google. Same thing happened to my html section also. So I am concluding that if I am adding some content to an old section it is doing well and when I am adding a new section and adding content then it is not getting visitors from google.

My home page has PR3 and all my old sections have also PR3.

What I am thinking is Google takes time to give PR ( internal, not visible ) to a new section so it will take some time to get its due importance from google. Is it true that google also maintain rank of inside sub sections (with directory ) within a site and give good rank to a new page of the old section ? So is it always beneficial to add new content to an old section than adding new section and new content?

Your views please.