Because your users need (especially in large environments) need enough time with version 2.0 to plan and implement their migration to that newer version. In fact with most software companies tend to skip a version for that very reason.
e.g. My last shop did not go to RHEL4 from RHEL3, they waited for RHEL5. If they did not do this they would constantly be updating their OS's to new versions not improving their infrastructure.
ack, not software companies but companies that have a large software infrastructure.