I, myself, have a house rabbit, and can attest that she can be quite disapproving. But given my typical (ahem) scientific nature, I'd rather explain my theory on the nature of this supposed apathetic bunniness and put forward a commentary on it's societal impact, as well as a sort of call to bunny-arms.
First, let's get one thing straight: a rabbit is not a rodent - it's actually most closely related to the llama. Yes, I said llama. Rabbits belong to the order Lagomorpha, which was properly identified in the early 1900s. They share several characteristics with rodents, including their ridiculously-long growing incisors - but beyond these superficial similarities, most owners of both rabbits and rodents will attest that they are very different.
Before I became caretaker to rabbits, I always fancied them like a hamster or a rat - similar in temperament and intelligence... not to slight them, but I never held rabbits on the same intellectional/emotional shelf as cats or dogs. How wrong I was! I think Abigael will always dissaprove of me for that.

Rabbits are actually quite sophisticated creatures, each with his/her own distinct personality, likes and dislikes, routines, etc. My Abigael, for example, is quite the diva - and not only mildly disapproves, but is sometimes downright disdainful. She has elevated The Cold Shoulder to an art form: she'll turn her back on you, then look over her shoulder to make sure you're watching... look away, thump very loudly twice, look back to make sure you're watching... a few more thumps... a quick shift to make sure her back is squarely to you...
I've encountered nothing so simultaneously condescending and adorable.
I'm not being entirely fair, though - rabbits can also be very affectionate and snorgling. Say "bunny kiss?" and Abigael will almost always be on your nose with her soft bunny tongue (unless you're already getting The Cold Shoulder). My Lizbeth was never happier than when neatly fitted into that perfectly-sized bunny nook formed by your thighs when you sit Native-American style on the floor.
So... how do you know when a rabbit is happy?
Well, they purr. It's not a traditional purr, but it means all the same things as when a cat does it: either lots of happiness or lots of pain. To "purr," bunnies rhythmically grind their teeth. Weird, eh?
Given her relation to llamas, as long as she's not spitting on me, I find my rabbit to be very approving indeed (no, she doesn't actually spit on me). So why does she seem so very disapproving?
I think it's mostly in the eyes.
For one thing, rabbits being classic prey animals and us being classicly predatory, the shape of their face doesn't speak to us. Looking straight on, a bunny face, with the eyes set on the side of the head, gives us a face full of nose and mouth - those least expressive and hypermechanical organs which artists emphasise when they want to heighten disdain and a lack of sympathy in their subjects (think political cartooning). We want eyes. Frontal, expressive eyes, which give us our window to a kindred soul.
But then even from the side, rabbit eyes aren't expressive to us. To our predator's instincts, we see the eyes of prey - seemingly cold and unresponsive. Partly this is because the whites are mostly hidden so there's not a lot of movement in them; really it's because rabbits are prey animals. This is our hard-wired instinct, which helps us to survive by separating our predatory instincts from our protective or empathetic instincts, and which has evolved over millions of years of a hunter/gatherer lifestyle to give us a willingness to eat cows but be repulsed by the idea of eating, say, dogs. Most of the animals we've chosen as companions are natural predators: cats, dogs, rats, birds... we understand them and anthropomorphise them easily. Rabbits are more of a challenge - we see them as very cute, but the anthropomorphisation is a bit clunky. Thus, in their asymmetrical cuteness, they seem disapproving.
What does this mean for us and the rabbit? Well, they haven't got quite the foothold that cats and dogs have in our lives, but they're gaining. And rightly so - a house rabbit is a wonderful companion, far more intelligent and caring than we've accredited them in our social circles, and, in their quirky way, right up there with cats as a meaningful pet. Having lived with house bunnies, I do hope they start catching on. They're easily litter trained, can be walked on a harness (with patience), and can even learn tricks. And, really , they're simply adorable.
Be sure to check out Disapproving Rabbits for some fun pix, videos, and a skootch of bunny education.
Also check out my Abbi's spot at Bunspace - she won't disapprove.