There're two sets of key layouts, between which you can easily switch:
"Modern", shown in most screenshots in the document, is not recognizable to HP users, I agree.
But give it five minutes, and you'll see that it simply trades what non-HP users would consider cryptic text (STO, RCL, SWAP) with iconic symbols. After those five minutes you may agree it makes the (tight) space look less cluttered.
You may also find that you like the Enter in the middle (simply because that's where your thumb likes to rest when holding an iPhone or iPod touch), and you may like 9 (instead of 6) soft-keys.
This mode looks daring, I know, but it's the result of holding the device and experimenting for quite a bit.
"Classic", shown in a couple of screenshots, too, is *exactly* the HP-28S key layout and key caps. Except CHS became +/- and USER became VAR. (Some 2nd level functions moved.)
I don't know what your HP reference is. A 41 sure looks quite different from a 28.
Finally: you can change the keycaps and the function of *any* key. You can even add or remove keys. You could even have a single-wide Enter key, but that would be crazy, of course... ;-)
Edited: 21 Mar 2011, 7:45 p.m.