There is nothing that, strictly speaking, prohibits you from sending such an email. However, sending such an email is unlikely to have a positive effect on your chances of admission. AdCom automatically assumes that all who choose to remain on the waiting list are still interested in attending Wharton. Thus, sending in the email would not really provide any new information.
Realistically, the intention of sending in such emails is typically to try to get some sort of "leg up" over other candidates: for example, through expressing one's presumably greater interest in Wharton by being seemingly more proactive than others on the waiting list. If no such advantage were realizable, I doubt anyone would even entertain the idea of submitting an email of the type you mention, above. So I am not sure sending such an email would be consistent with an ostensible desire to maintain fairness to all candidates on the waitlist.
Understand also that the waiting list is not ranked, and thus indicating one's continued interest in attending Wharton is unlikely to provide any additional advantage to the candidate reiterating their interest. If there is no such advantage or benefit to be gained, then writing the email is probably not worth the effort and time.
Indeed, the waitlist is better thought of as an unranked pool of very skilled and talented applicants. From this pool, certain applicants may be selected if they have particular characteristics or backgrounds desired to complement the makeup of the Class of 2012, as it currently stands. For example, there may be insufficient students interested in, say, public sector opportunities, and so the AdCom may consider filling out remaining spots with some individuals with such an interest. Degree of interest would not really factor into this calculation.
Hope this helps.
Victor M. Lee
Class of 2011