OLTP is for transactional systems, such as you would find on a baseball coach's "play sheet". It shows every pitch, swing, etc. because the coach needs to look at that level of detail... They need to know which players bat well agains left handed pitchers and whne an opposing left fielder frequently fails to catch balls hit by right handed batters.
OLAP is for analytical systems, such as you'd see on the late night news. It shows the final scores of the games and possibly the team position in the league. At this level of detail, people are interested in which team won the game, and who is likely to play in the World Series.
The OLTP and OLAP systems track different information about the same system. The informaiton is at a different level of detail, and the OLAP system is derived from data in the OLTP system, but they are truly different systems tracking different information instead of just different levels of abstraction for a single thing.