I wouldn't say Americans are more tolerant in general, however I suspect they are in the California area. I've met a lot of Americans who are very intolerant of broken accents, the same seems to go in Canada too (where I currently live). People in the Greater Toronto Area can be much more intolerant of accents, where as people from the Atlantic and Prairies seem much more tolerant.
I don't know what causes this intolerance, however I believe it may be caused by a lack of exposure to different accents. I tolerate accents very well and tend to have a chameleon-like ability when it comes to moving between areas. However, I regularly visited France growing up, I had Scottish + Welsh + Irish teachers throughout high school and have visited lots of European countries, so I wonder if it's simply due to lack of exposure.
I have to say I do not have a bad experience with English people. I am actually very fortunate that I have a lovely colleagues who accept my English.
The only criticism I get on social sites and via email. But as long as they are right I cant really complain.
What I've found out is that while Americans are a lot more insensitive (tolerant?) to broken accents the British absolutely can't stand it. They avoid talking to people with bad accent and will generally walk away form any conversation with somebody of a non-british accent. I've observed this with brits around the world, not only in the UK and for sure it's not related to talking among conationals only: generally they are willing to engage in conversations with people that are obviously not british as long as they speak proper english with proper accent.
Of course you can not generalize the above to every brit in the world however this is my observation.
About blogs I observed in a comparative study that pages not ending in .com are just a bit less likely to be clicked.
About a written message, what can I say? If the English is badly broken I get annoyed too. If there are minor spelling mistakes it does not bother me, substance prevails over form.