In the Stack Exchange model, the question is supposed to be just that - a question. Editing/adding information should be done for clarification; edits should make a question easier to read or provide relevant information essential to solving the problem. A summary of answers, or responses to answers, are not part of a question.
These types of edits are more appropriate as other actions:
- Thanking answerers for their response and helpfulness:
- Upvote useful answers
- Accept the most helpful answer
- Comment on the answers (although "thank you" comments are not generally encouraged, they are certainly not harmful)
- Award a bounty to excellent answers
- Contributing to/improving an answer:
- Comment on the answer to suggest an improvement
- Edit the answer
- Asking for clarification or further answers:
- Comment on existing answers to ask for clarification/explanations
- Edit the question to help those answering to better understand the problem
- Start a bounty on the question to attract more attention
The question and its answers are intended to be resources for future visitors to learn and to understand how to solve a particular problem. Questions are always open for more answers (exception being closed questions, which we don't want anyway), so the summary of answers may someday be obsolete if a new, amazing answer comes along. Additionally, usernames can be changed, so someone may say "Hm. The question says user1234567890's answer is really wonderful, but there is no answer from a user1234567890."
Additionally, the "help" provided by this type of summary is redundant, repetetive, and unnecessary, and not really needed. The question describes the problem. The answers immediately below the question describe solutions. They all have a score next to them based on community voting (experts saying "this is a good solution to the problem" or "don't listen to this, it is incorrect"). The asker may have gotten a solution to their particular instance of the problem, but still not understand the issue as well as other experts in the field. The accepted answer may not be the best, and the answers summarized in the question might not be that great. The expertise of many users viewing the question and answers over time will provide useful insight into what is actually the most accurate and complete solution.
These edits don't add anything constructive to the question to help answer it, duplicate content already on the page (as of a specific time), and make the question a bit harder to read. It is not an appropriate use of a question.