Obviously, before emailing anyone, you should first search the web for any manifestos or policy statements that they've written on the subject of communication. Not doing so is terribly rude.
By emailing an individual directly when there is a proper support route setup you are basically shouting "Oi you, developer type, this is my priority and it should be your's to, I don't know what else you are doing, but you should look at this". You are a cold caller. You are the restaurant customer who snaps his fingers and loudly calls "Boy!" to get a waiter's attention. Yes, you are being rude. Don't expect me to be glad that you chose to grace me personally with your message.
The easy way around this I find is to prioritise things that have come through the proper channels. I don't ignore direct emails, but they don't get looked at quickly (especially if they have the "urgent" flag set) and when I do respond I point out that they would probably have been dealt with yesterday (or last week) if they had used the preferred contact point. In a commercial setting our SLAs don't kick in until an issue is raised through the right channels, so it is in your interests to use the right contact method.
The right answer to a phone call informing you that the email a user sent two hours ago is urgent? "Well then it is urgent that you raise the issue the right way, would you like reminding of the support portal's location?" (or for certain requests "would you like reminding of your project/account manager's phone number?").
Yes, this is why I'm generally not directly customer facing and a method I use in order to ensure that I remain not directly customer facing!