It's actually the reverse when it comes to licensing (or contracts for the matter). If you don't explicitly state it, then it can be interpreted to be implicit. When dealing with licensing or contracts, you want as little legal wiggle room as possible. Part of the reason even the most basic of contacts/licensing are pretty verbose.
There is no sale here. Do you have an example of someone being held liable for code they gave way, or some analysis by a lawyer or judge saying someone in such a situation could be held liable?
http://en.wikipedia.org/wiki/Implied_warranty