In defence of our colleagues across the pond, it's not a 'my plane is bigger than yours' thing but it is written in the FAA rules somewhere. Here are some examples.
http://www.faa.gov/air_traffic/publi...c/atc0204.html
-4-14. WORDS AND PHRASES
a. Use the words or phrases in radiotelephone and interphone communication as contained in the P/CG or, within areas where Controller Pilot Data Link Communications (CPDLC) is in use, the phraseology contained in the applicable CPDLC message set.
b. The word “heavy” shall be used as part of the identification of heavy jet aircraft as follows:
TERMINAL. In all communications with or about heavy jet aircraft.
EN ROUTE. The use of the word heavy may be omitted except as follows:
1. In communications with a terminal facility about heavy jet operations.
2. In communications with or about heavy jet aircraft with regard to an airport where the en route center is providing approach control service.
3. In communications with or about heavy jet aircraft when the separation from a following aircraft may become less than 5 miles by approved procedure.
4. When issuing traffic advisories.
http://www.faa.gov/air_traffic/publi...4/aim0402.html
5. Air carriers and commuter air carriers having FAA authorized call signs should identify themselves by stating the complete call sign (using group form for the numbers) and the word "heavy" if appropriate
For info, having heard my first Super designator over the Canada last night.
FAA Issues Interim ATC Procedures For Airbus A388 Flights