This week's book giveaway is in the OCPJP forum. We're giving away four copies of OCA/OCP Java SE 7 Programmer I & II Study Guide and have Kathy Sierra & Bert Bates on-line! See this thread for details.
Each database is different, and despite all attempts to standardize database access, there are always differences, be it because certain vendors have deviated from agreed upon specs, or because some vendors just implemented something wrong. The dialect compensates for this, and helps make Hibernate as database agnostic as possible.