In a country that does not allow prayers in public school, I find a religious invocation at a national convention* from any denomination a bit strange.
*PARTY CONVENTION AND GENERAL ELECTION GRANTS
The Presidential nominee of each major party may become eligible for a public grant of $20,000,000 plus COLA (over 1974). For 2012, the grant is approximately $91,241,400 for each major party nominee. With the exception of the 2008 Democratic presidential nominee, Barack Obama, every major party nominee has accepted the general election grant since the program's inception in 1976. Candidates themselves may not raise any other funds to be used for campaigning during the general election period.
Public grants of $18,248,300 went to each of the major parties for their conventions in 2012