Yes, steemit account is included. I don't know of any reasons for not doing so.
It is certainly an outlier. There aren't any other accounts that have a significant portion of their holdings specifically earmarked to be given away to new users. Another significant portion is earmarked to be sold to provide funding for development. Both require powering down, meaning that any powering down by that account is not a discretionary decision being made on the basis of desire to reduce investment (or transfer stake between accounts). Power downs for the purpose of creating new user accounts do not lead to selling at all (though this would also apply to other power downs intended to power up another account). It isn't owned by a person, it is owned by a company, and we don't know how many owners the company has. Finally, that account also does not vote, so it has no bearing on the distribution of content or curation rewards.
Those are some of the reasons to not include it. On the other side, some of its power downs do hit the market, so it is meaningful to include it in that sense.
It doesn't make sense to me to exclude the largest owner from the ownership table, or the power-down metrics.
Giving a tiny fraction of coins away, or paying for development are all good causes - but not good enough to pretend that the money doesn't exist.
The budget for coins being given away is not 'a tiny fraction', it is half of all the coins in that account. I'm not suggesting that the money doesn't exist, although that is one perspective too. Since the account is part of the platform design, it isn't entirely unlike the undistributed coins (currently about 5 million) in a system like Bitcoin. If Bitcoin had an "undistributed coins" account on the blockchain would you include it? It would be the largest known holder of Bitcoins.
Anyway, my primary purpose in raising the issue was not to argue whether it should or shouldn't be included or how, it was primarily to ask that it be clearly stated. For example, in the statistics on steemd.com/distribution, the steemit account is not included, but that was not specified until I asked that a clarification be added. Now that it is clear, those statistics can be interpreted accordingly. Likewise with yours.
To me it would seem the equivalent of adding @null to similar SBD analysis.