Artoomis:
Your point about the about the intelligence of the PHB writers is actually beside the point - at least for me. For me, the question is "what is the rule?" Not "what should the rule be?"
Actually, to do this, you would also have to prove that the rules do not elsewhere imply that you
do get an extra 5' step with
haste. Otherwise you have merely pointed out a rules inconsistency, and you will have to fall back on "the intent of the game designers is..." And then, no matter which way you argue it, you'll probably conclude "you know, they could have phrased all of this a lot better," which is what I was talking about with the PHB writers.
Also, you rely way too heavily on the glossary quote. I personally don't see a glossary quote as authoritative, and can be easily outweighed by what's in the actual rules. The argument against: the glossary is speaking generally, since it's rather half-assed.
That's the question I, at least, am trying to answer. An I've answered it, using three different quotes from the PHB that deal directly with 5-foot steps.
I don't think so. Your argument goes like this:
(1) You avoid an AoO if your entire move for a round is a 5' step.
(2) 5' steps MUST ALWAYS avoid AoOs.
(3) Therefore, if you
could take two 5' steps in a round, then they would both avoid AoOs, and this would violate the rule on p. 117 interpreted strongly -- so you can't do it.
Let's call this argument the "I'm sorry, I'd love to move five feet, but I feel like I might provoke an AoO by doing so, so it's somehow impossible" argument.
Your argument hinges on step 2, which relies on your interpretation of the glossary entry, which someone going against your argument would call over-literal, because it's clear that
haste is a special case that requires the interpretation of rules that were not written with it in mind.
Step 2 is weak in another way too:
Counterexample:
Hasted fighter, threatened during whole example. The fighter does this sequence of moves:
Standard Attack: (Move 5', attack).
Partial Action: (5' step, attack)
Note that the fighter has only taken one 5' step in this round, because the first movement is
not a 5' step. If you rule that it is, then what about this sequence?
Partial Action: (move 5')
Std. Action: (attack, move 5')
This is legal in anyone's rules (except maybe SpikeyFreak on a weird day

), but not if you try to be strict about interpreting 5' movements as 5' steps. Note that if either only the partial or the standard action were performed, you would call them 5' steps and no AoOs would be drawn.
I think the quote on p. 117 does nothing to imply that you cannot take two 5' steps in a round; it merely implies that if you move 10' in a round or more, you don't avoid AoOs for moving.
But even this quote may be undermined by pointing out that it was written with the assumption that you'd never really be able to take two 5' steps in a round anyway.
The reason that it seems "stronger" than other rules is the broad, general way it is phrased, something like "whatever else happens, if you move only 5', that's how you avoid the AoO."
I don't think you have a good case for "the rules say no extra 5' step with
haste, beyond a doubt."