Not really sure how to answer that un-circularly. They’re two-stroke radicals because they’re drawn with two strokes. (I assume you’re talking about the radicals, in any case – the kanji for stairs is certainly not a two-stroke kanji.)

Granted, the images shown don’t really make that apparent, and this is kinda where Koichi’s reluctance to teach how they’re written comes back to bite you.

Edit:

Actually, on second thoughts, now I’m confused too. I haven’t been able to find Koichi’s “beggar” radical in any official list of radicals anywhere, and the character for beg is 乞 – a three-stroke character. Koichi’s radical might be a simplified version of the character used in some of the more complex kanji (in the same way the “liquid” radical is a simplification of the water character) but I’ve not been able to find any examples. Considering 乞 is one of the joyo kanji, I’m not too sure why It’s not in Koichi’s list of three-stroke characters – maybe it’s falling foul of his 80-20 picking and choosing.

• This reply was modified 12 years, 11 months ago by  Joel.

Ah, I found the “beggar” radical. It’s a variant of the “enclosure” radical. I haven’t been able to find it as-is, but with extra strokes included, it appears in characters such as 写真 (しゃしん photograph) and 汚い (きたない dirty).

Yah, I tried jisho first, but it’s missing Koichi’s “beggar” radical. Mind you, so’s the radical cheat-sheat on tofugu – I wonder if this particular radical is a recent addition.

You can find 写 here, though: http://www.jisho.org/kanji/details/写 – the “beggar” radical is the third and fourth strokes.

Here’s textfugu’s article on 写. I have to admit it might confuse matters, because (right now, at least) he’s described it as being an assemblage of the “forehead”, the “enclosure” and two “ones”, a total of six strokes, but it’s a five-stroke kanji (and he’s got it listed under his five-stroke kanji too). This is probably why he created the “beggar” radical, so that he can change this character to being “forehead”+”beggar”+”one”. Anyway, linky: http://www.textfugu.com/kanji/5-stroke/写/

P.S. Koichi? I like the radicals approach, but if you’re not going to cover the strokes at all, it’s only going to confuse matters.