Interesting perspective you have. I agree on a very limited basis. We support each other but just not in a sense of "shopping". We really support each other in everything.
The other sites you will note are limited in their training. One site just opened up a training center very similar to Hub Pages.
Additionally, the technical support with HubPages is outstanding - writing to email@example.com is always very responsive. The capsules are simple to navigate and allow a professional looking Hub to be created in no time. Copying a "master format" with the capsules you always use such as a news capsule at the end after comment along with a links capsule can simplify the process and allow the writer to concentrate upon the writing.
Oh, and the photos are another method HubPages is better - your photos are stored.
The forums offer a world of help complete with a specialized forum just for critiques.
The benefits of HubPages have it poised to be a site that even Google is envious of. If you compare page rank among the other sites, you will see for content, HubPages adhere to high standards of quality.
HubPages is better than pen pals and for me has proven to be the best business partner. It is a money maker IF you wish. It is a site with lasting friendships, it is a training vehicle for promoting yourself and your website on the Internet. It is not really free, the time commitment is demanding.