First I have to say, that I like all Atlassian product. Especially because of the well integration between your products. It is easy to find relevant information and navigate between the systems. E.g I can navigate from Jira to a Bamboo build regarding the selected issue. Or I can see the build and test results of Bamboo in my build tab of the issue. Perfect!!
I think the reason is, that the Atlassian strategy wants to make things easier.

No I found something which conflicts with your concept regarding Stash

• I have an Issue and the regarding code changes in an Git Branch.
• Now I have created a Pull Request in Stash and of course somebody should review my changes.
• The review was successful and I have merged the branch into the master over Stash.

PERFECT usability, but:
From the Jira-Issue view:

• Where can I see that the Pull request was approved?
• Where is the "green/red color" which indicates the state?
• How can I navigate directly to the relevant Pull request? The number is available, but not a link. I can navigate to everything (Project, Repository, Source, Commit) but not the important Pull-Request. It is possible to navigate from the Pull request to the issue but not from the issue to the Pull request.

I can not believe that this is not implemented..... This follows not the Atlassian strategy "Make things easier"

I hope this functionality will come soon. It is a must...