Hey Jim,
I spent some time trying to figure out the details and wasn't able to come up with a satisfying answer - but after thinking about it some more - I realized my last answer was a little bit off base (i thought you were not seeing the styles reflected when the page was rendered...) and that it's probably just an issue with the FCK Editor itself (which is what is used for Text/HTML module).
I'm curious to know why it works in the other version of DNN you are using, because it should still be FCK Editor in 4.5.3.....
In summary, I don't think FCK Editor currently provides this functionality, but I wasn't able to come up with much detail!
Take care,
Ian