A senior executive, frankly, has more capital to spend. If he dresses slovenly, it's his perogative. Being in middle management, I have to get up and conduct all the presentations, stand at the front of the door to greet people for my meetings, meet vendors, etc. Dressing well helps with the presentation technique. 9 out of 10 times if someone new to your office is lost or needs something, they'll go to the best dressed person. If you want to hide from contact and clock in 9-5, then dressing like the masses helps.
I just started at a new office. Bringing my suit + no tie or suit + tie but jacket off has already made a lot of people in my group step up their dress and take their jobs more seriously.
Vis-a-vis a three piece, I work in a support department in insurance and at my old job carried it off once a month excluding summers. I got a few comments at first but no one paid attention at the end. I see people wear suit & tie for customers and since the people who work in the company are my internal clients, I'm dressing as part of my service to them. I learnt that from a contractor in London who would corral network cables in a suit and tie because to him anyone who pays him is his customer and that's the image he presents to the customer.
Someone else posted this in another thread and I remember the comment was how this was a great social experiment.
I wear a suit and tie every day, which is how most of the folks four levels over my head dress. I would have no issues with wearing a three piece, and I have never seen anybody at my company wear one. Most of the people at my level wear a dress shirt, trousers and sometimes ties. I get a lot of compliments, and I can tell people even over my head treat me with a certain positive respect. I have never preceived any negativity from anybody because of "over" dressing. I think it all comes down to how you hold yourself and your work performance. If you act like a dick, people are going to call you "that dick in a suit", if you suck at your job people will label you an "all show, no go", however like FDR said, "Speak softly, but carry a big stick."