What are the policies governing what is allowable in a user profile?
How much more lenient are they than what is allowed in a post?
There are a few of these on Meta.SE, including Offensive profiles - where to draw the line?; quoting Tim Post's answer there:
To be clear, we give people as much latitude as possible when it comes to their avatar and profile page. It's all about them, and we try to let them just be themselves.
When a profile page or avatar has, or is likely to create a disruption, we need to be made aware of it and investigate. We might not take action in some cases, but we really do need to be aware of it.
Our general approach has been to take a hands-off approach to the user page -- it's for you to place whatever you want there, within reason. Obviously racism, hate speech, any sort of overt evil will not be tolerated. But there is more flexibility in the grey areas on the user page, because it's about the user, not us.
Or John Rudy, from Rules for Profiles:
Generally speaking, your profile is (to an extent) fair game, as it is a reflection of you as a person, not the site as a whole.
There are reasonable limitations for all of those, but generally speaking, unless you're a hard-core spammer or you put something truly offensive / crazy in there (like hate speech or pornography), you'll be OK.
The general policy, as I understand it, seems to be:
User profiles are allowed more leniency (for things like expletives and self-promotion) than other posts
Content that could be reasonably construed as offensive (hate speech, for example) is Not Okay
I really think your answer is in your question -- the powers that be have pretty succinctly outlined what is and what isn't okay in a user profile. Perhaps others feel differently, though.
I use quotes, have an "about me" paragraph, and use images in my profile, which is located here if interested.