if you want to write an article about the number two tablets, the only way to do it is to exclude the ipad.
Not at all. You can show, and write, exactly what you just said one sentence earlier: "The iPad has 90% market share, and the other companies split the remaining 10%, with five companies each taking 1 to 2 percent of the market."
What about that is so difficult for mortals to understand?
Even if you never mention Apple more than once, it's important, when (e.g.) pointing to the fact that HP has almost twice the share of unit sales as Motorola, to recognize that you're comparing a 2% share with a 1% share, not a 20% share with a 10% share. There's a big difference between 1% and 10%, both qualitative and quantitative. For example: Smaller numbers are closer to the noise level, and therefore more subject to fluctuation. 1% could really be 2%, and could easily jump to 2% in the next quarter, but it's unlikely that 10% is really 20%. And, lo and behold, this turns out to be relevant to this very case, because in fact HP's numbers have probably been goosed by a one-time money-losing giveaway of Touchpads. That's a fluctuation.
"Why is this so hard for mortals to understand"
No need to be an asshole
Furthermore, don't you think a financial analyst would already know Apple's numbers? The target audience is not some Kid Biz article. Just saying.
Gruber's article is a counterpoint on "PC manufacturers are dominant in the tablet space", and the idea that NPD were incorrectly attributing the "number 2" player to HP. Naturally the iPad comes into discussion (and yes it's smart to remove the iPad when trying to look at the rest of the market.) However NPD were publishing conclusions that aren't reasonable in light of the fact that the Kindle Fire and B&N Nook are selling very well in addition to the dominance of the iPad. By some reputable estimates the Nook is selling well in excess of HP. (To the tone of 15x the sales of HP.)