Imagine that in the XML world there is already 2010, but in your relational world it's still 2009. This or the reverse could happen if you directly use fn:current-date() in XQuery and the CURRENT DATE special register in SQL. The reason is that XQuery by definition operates in and returns UTC-based time and date values, e.g., whereas the SQL context in DB2 refers to the local timezone.
To work around possible issues, user could call fn:adjust-date-to-timezone() to convert a data (or analogously a time or dateTime value) to a specific, e.g., the local timezone. Well, the world got simpler just recently. DB2 9.7 FP1 introduced new (DB2-specific) functions to retrieve values in the local timezone directly, named current-local-date, current-local-time, current-local-dateTime, and local-timezone.
Having different years in the SQL and XQuery context might be a rare event, but the usability improvements are very handy - not just close to year end.