The structural phenomena I found to be the most prevalent in the theme of this piece were cadences, tonality, and motive. Most of the cadences are clearly noted and easy to pick out. They are often accentuated by dynamic changes at the beginning of the new phrase following the completed cadence. The piece begins in a solid D major, but after the repeat/double bar at the end of measure 8, Mozart plays around in the dominant key for a few bars before returning once again to D major. Also of note, there are no tempo markings in the score, but the performer of the particular recording I listened to leans on the first beat of the last measures of phrases, thus creating the feel that the piece is slowing. The cadences feel much more final to me because of this.
Motive is a very important part of any theme - it gives the listener a solid foundation that is then elaborated upon in the variations, so a clear theme is essential. Initially, the motif in this piece is introduced and then repeated before continuing on to the short phrase that contains the tonality change. Finally, The theme is stated once more but in a shortened version for the last four bars of the tema.