If I buy software at Best Buy, I do have an implied contract, governed by the UCC, to pay them money to be allowed to walk out with the software. But the license itself is not a contract.
In other license cases, such as BSD or GPL, or when downloading other freeware or shareware (until registered), there isn't even that implied contract. I just use the software under the license granted.
The license agreement, which governs your use of the software and details what the conditions for having a valid license, is a contract. Don't confuse the license - which is simply a grant of permission to use the software - with the license agreement, which details how and when that permission is granted to you - that agreement is very much a contract.