The Server Fault site is part of a project named [Stack Exchange][1].  [Stack Overflow][2] was the first site implemented using SE.  The SO site was also the first to have a related *meta* site for discussion *about* SE/SO itself.  [The MSO site][3] is where you will find answers to any "*what, why, how*" questions regarding the behavior of SE-powered sites -- in particular, the ["Official" FAQ][4].  The "rules" of the SE sites were not arbitrarily chosen in private.  MSO's discussion history chronicles the development of these rules as well as the Community's reaction to them.

 1. Reputation requirements for commenting is an implicit design choice of SE.  You can find discussion of this on MSO.  For starters, right from the [FAQ][5]. Additional searches will reveal other related discussion.
 2. Actually, comments *do* [support formatting.][6] Yes, a limited sub-set of "regular" formatting, but formatting nevertheless. Comment formatting was [discussed on MSO][7], and although not a popular question, it succinctly captures the *purpose* of comments *vs* support for full-formatting.
 3. An *answer* is intended to be an *answer* and *comments* are intended to be *comments*.  Discussion at MSO has repeatedly clarified this.

But to address your first question:

> I know that I can answer and I
> initiate the answer starting from
> clarifications immediately getting
> negative ratings which discourages to
> further participate in this thread.
> 
> What's the point in this?

The point is that all the SE sites are *Community-driven*.  What is considered acceptable content and behavior is decided by the same Community that uses and contributes to the site.  Insistent and intentional deviation from the Community's expectations will result in down-votes. As with any Community, some may grow tired of what they perceive as unwanted behavior.

I would *highly* recommend dedicating time to exploring the MSO site to understand not only the functionality of the SE software, but also the expectation of participant within the SE Communities.

  [1]: http://stackexchange.com/
  [2]: http://stackoverflow.com/
  [3]: http://meta.stackoverflow.com/
  [4]: http://meta.stackoverflow.com/questions/7931/the-official-faq-for-stack-overflow-server-fault-and-super-user
  [5]: http://meta.stackoverflow.com/questions/19756/how-do-comments-work-in-stackoverflow
  [6]: http://meta.stackoverflow.com/questions/2115/text-formatting-now-allowed-in-comments-list-of-proven-and-disproven-abilities
  [7]: http://meta.stackoverflow.com/questions/20584/comment-formatting