A favorite (alas unpublished) theory paper of mine shows:
He who pays the piper calls the tune, but he can only successfully call for a tune that he will recognize upon hearing. … When experts must pay to acquire information, have no intrinsic interest in client topics, and can coordinate to acquire the same information, no expert ever pays to know more than any client will know when rewarding those experts.
So why should you ever believe what you read? Consider “Avoid bridge, construction delays.” The newspaper might fear that you will try the bridge, and think less of them if their forecast is bad. Or they might fear that your close friend will, and tell you.
How about “Michael Jackson arrested today”? Few readers would normally check this firsthand, but if a big story like this was wrong then a competing publication might make a stink, and then one of your friends might check it out. For the vast majority of media claims, however, there is little incentive to make a big stink, and few people who care would ever learn the truth given a stink. So if it takes the media much effort to learn the truth, why should they bother?
Media watchdog charities might claim to check for you, but why should you believe they share your interest in knowing the truth, instead of just wanting you to write them a check? Bloggers can also claim to help you check, but if those bloggers mainly care about attracting readers (an interest MR and others often admit), the same problem remains.
The only real solution I can see is to make better use of the people you have good reason to think really do share your strong interest in knowing the truth about some topic. So connected blogs by people who know each other in other ways may be the key. Perhaps such networks lower the cost of raising a stink to the people who care.
Of course it may also be that most of us do not really care about the truth; we might just want interesting new things to talk about with each other. Which might explain the otherwise-surprising lack of interest in this problem (which applies to academia at least as well as to the media).