Even when i first started developing websites in college (95 - 96) one of the biggest items was to make the site compatible for multiple browsers. Heck i was even developing the sites to be compatible with text based browsers like lynx. As this progressed you would even see sites get soo crazy to have completely different websites based on IE or Netscape (back then) (this was of course over kill)
However, that started to change, especially with intranet sites. At that point, companies didnt care they could control everything and started to only develop sites in IE.
I am starting to see this scary trend continue. At a client one of my friends was at he was forced to put out a site that was IE only. (wth). This is just baffling to me. Especially the fact that this is a heavily interactive site where they are to generate sales from. And not only that but they were trying to target younger computer savy audiences. You know those most likely to use firefox, opera, or safari NOT IE. Even with Netflix, this trend is continuing. Sure you can get movies online, assuming you only use windows + IE. Why is this?
Are web sites getting soooo complicated you can't develop them for multiple browsers? .. No .. the fact is there are sooo many tools out there to support cross browser productivity that this is by far not a reason. Time schedule? Eh this maybe an issue, but i don't believe so either.
The answer ... as one friend put concerning the netflix site, "lazy developers". Or i would expand, lazy unskilled developers. The reason i discount the time, is that for the most part MANY of these issues (maybe not as much with netflix) but other sites is the fact that if you follow best practices you are not going to have loads of browser compatibility issues. People need to start to demand more from their websites and not settle on mediocre development!!!