http://www.cdc.gov/nchs/data/databriefs/db88.pdf explains all of it. in 4 years you will have a noticeable number of registered Republicans die. In 8 years you will really be aware of it. They must be replaced! The numbers of missing voters demonstrate nothing more than a failure of the party managers to replenish the supply of voters!
Our school systems are producing Dem voters as well. They serve as indoctrination centers--both K-12 and higher education.