yes, I do think that all email that are sent as personal need to be the same for work based. I think that an email needs to be a professional appearing document, so that the person will think that you are educated and that you will not look like a child.
Personal conversations have always held a different aura about them than work based communications, and these same rules should apply to new age technology such as emails. When an individual is addressing a colleague or boss, they are going to be using more formal and codified rules of conversation than if the same person were to be chatting with a friend.
Email netiquette should be observed even though it doesn't have to be simply because we have freedom of expression. There are guidelines for using certain email systems, but those aren't based on Internet etiquette. If someone doesn't like policies or guidelines with regards to certain email providers, then someone can go to another company or just create an entirely new email system.
It's common sense that one should practice netiquette for all email accounts. One never knows when an email could be forwarded to the wrong person. Still, a personal account is personal, and sometimes people may joke or send inappropriate photos etc. That's not a great idea, but work accounts definitely require much more and more constant minding one's manners.
I do not believe email netiquette for persona accounts should be as stringent as that for work-based accounts. Personal accounts would have a barrage of common communications between friends and family that are familiar with each other. I believe the precedents of those communications should be set by the individuals in those conversations.