That's an easy one. They've been reflexively spewing vitriol for so long they've forgotten how to read for comprehension.
That is true. Here is the process many users have developed as a reaction to new posts on Macrumors:
1. Click "Negative" on Story
2. Read first paragraph to identify target of aggression (AT&T or Apple in most cases)
3. Post a negative message about the appropriate target. It does not matter if this post is topical or in any way relevant.
4. Watch for replies quoting your post so you can call people fan boys.
A few of them use a little more style, but they still follow the exact same formula.
Here is an example story and this type of users response process:
Story:
Apple and AT&T have teamed up and found a cure for cancer in kittens.
Process:
1. Click Negative
2. Story is only one sentence, read the whole thing!
3. Post Reply:
Apple and AT&T suck, Verizon has been curing cancer for years with their Android phones. Steve jobs just wants to control kitten cancer so he can screw you over.
4. Wait. A reply: "Wow you seem a little off, mate"
5. Respond!:
**** Fan Boy loser. I bet you wear a black turtleneck.
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We see this precise process played out over and over.