I think there are some other reasons to use Title Case vs. sentence case in UIs:
Shapes, not Words
One should not make the mistake of equating readability of commands with usability in all cases. Yes, it’s true that sentence case is easier to read, but after a certain amount of time, we no longer read the text on buttons, but instead pick them out quickly based on the whole shape of the text string. In other words, I’m not looking for Show all records vs. Filter records, I’m looking for the shape created by Show All Records vs. Filter Records, which look very much different from each other due to the differences between the letter S and F, and the big A in the middle (one could also make them Show All Records and Filter to make for an even easier differentiation.)
Content vs Chrome
While it’s true that sentence case makes it easier to see proper nouns, I don’t see a lot of proper nouns in UIs (with the exception of ‘About <product name>’, and introductory text like the example you gave.) What I do see all over the place is the need to differentiate content from chrome. Content here is defined the stuff in your fields, Name, address, etc. Chrome is labels and buttons. While most UIs make these 2 sources of text different via font or style (or both), anything else helps.
First Name Fred
Looks a little clearer to me than:
First name Fred