The UML has had plenty of updates in the past 10 years. For the most part, it has been valuable to follow along as the spec moved from one version to another. I've been following the spec since v0.8 or v.9 as I was working for Fidelity Investments in the early 90's and they were early adopters of the UML - my first UML class was taught by Grady Booch.
UML 2 has some really good stuff in it. It formalizes the region notation and timing tick marks people have been improvising on the sequence diagrams for years. I also think the current thinking on using stereotypes is an improvement and moves us back to a more deliberate engineering notation and away from the UML becoming confused with clipart. I also find the expanded component notation to be really good stuff - balls, sockets, ports, nested components, etc.
Still, it can be handy to revert back to older definitions of the standards. You might do this for tool reasons. A product claiming to "support" UML2 probably only does so partially and often is taking advantage of that UML2 preserves lots of UML1 notation. Or you may be trying to make sense of the features that have worked their way in and out of the notation.
Whatever the reason, I like to keep some of that older UML material handy. Most of this material can be found with a little bit of effort by searching the OMG website but I also keep copies handy in the UML section of my personal website - copies of past and current UML specs are available there.