There are two distinctions among beasts, animals, and magical beasts that I see as useful to different degrees. The distinction between magical beasts and beasts is actually the less important one, but it does seem odd (and certainly more confusing than not calling a dinosaur an animal) to regard something as a "magical beast" when it has no magical properties. This might actually be solved if the type they had eliminated were magical beast, and they'd just called all fictional animal-like creatures beasts whether they had magical powers or not.
And to really be fair for a second, I dislike the stated reason for the change (the business about dinosaurs) far more than I dislike the change itself. But then, without being able to see much of an other reason for the change, I see it as mere tinkering, and I don't see mere tinkering as a good thing.
The distinction between animals and beasts seems critical to me to maintaining the appropriate flavor of animal-affecting spells and class abilities. Owlbear animal companions would be right out for me.
Basically, with the announced scheme, you end up with either non-animal animals or non-magical magical beasts.
Back to the original question, the distinction between giants and humanoids is useful mainly because giants are a clearly identifiable mythological archetype with reasonably diverse variations, and it's convenient for creature types to match those kinds of classifications. I see having a description for what qualifies as a "giant" more complicated than "giant" (yes, even "humanoid (giant)") as kind of pointless taxanomical pedantry. Granted, humanoid subtypes act essentially like types for most relevant in-game effects, but would making giants not be their own type actually be a simplification? I don't see it that way.
And you clearly don't win by defining "giant" as just those creatures so indexed in the monster books (i.e., excluding ogres, ettins, trolls, and such, as has been suggested somewhere). I'm running a giant-based campaign (in the environs of Geoff) and it's incredibly helpful that I have some flexibility in creature types, and CR's that range from 2 on up. Not that everybody has that kind of requirement, but I think that sort of expressive range is a good thing to have in your game.