That is the limit with InfoPath out of the box data connections.
Instead of custom code you can also use our DBXL (database acclerator) tool to submit your data to a DB without the 255 char limitation:
http://www.qdabra.com/en/products/DBXL.aspx
Integration with DB's can be time consuming, DBXL will really make your job a lot easier than custom code or the built in data connections.
Ted