On the High-3 Retirement Pay Calculator, why would an E-6 that retires in 2009 (with 20 years of service) get paid around 1500 per month BUT THEN an E-6 that retires in 2030 (ALSO WITH 20 YEARS OF SERVICE) will get 3500 per month?

Take a look. . .
http://www. defenselink. mil/militarypay/mpcalcs/Calculators/FinalPayHigh3. aspx?calcType=h3