Free software does not mean public distribution. Free software means that the licensees have all of the four essential freedoms (http://www.fsf.org/licensing/essays/free-sw.html) with the software. Selling free software means that you license the software with a fee to a buyer under a free software license. With the four essential freedoms, if the buyer wishes, the buyer can license the software to the public without any fee (e.g., public redistribution via the Internet). Therefore, public distribution is not an obligation, it is a freedom that one can have with free software.

Now the question is: having been licensed a free software, is the buyer obligated to resell/redistribute (i.e., relicense) the software to another party privately/publicly with a free software license? If the free software is licensed to the buyer with a non-copy-left free software license (e.g., the MIT license), the buyer is free to relicense the software under any other license including proprietary license. But, if the free software is licensed to the buyer with a copy-left free software license (e.g., the GNU GPL), the buyer is obligated to relicense the software under a copy-left free software license.

In other words, licensing a software under a copy-left free software license like the GNU GPL increases the number of copy-lefted free software because one copy-lefted free software begets another copy-lefted free software whether the software is only used privately (within a single company) or uploaded via the Internet for everyone's benefit.

Now let's talk about profit. A software company can opt for either selling free software or proprietary software. If the majority of the buyers appreciate their freedoms, the software company is better off with free software. Using a noncopy-lefted license will bring no further benefit for the free software company. The reason can be explained by showing the sort of benefit that a copy-left license can afford:

1. More free software are available for reuse. With this, the software company can sell better and better free software. And, don't forget that reuse is _very_ important in delivering high-quality solution in a short time.

2. A scheme that is employed by MySQL or JobScheduler can be used. The scheme works by releasing software as copy-lefted free software to the general public without any charge via the Internet. The software company treats this as an advertising means for the software. Beside being an ads, this brings benefit to the software company as well because the general public will give any sort of feedback to improve the software further. Since a copy-lefted free software cannot be relicensed under a proprietary license, any proprietary software company that is interested in the software can ask the software company to sell the software to them under a proprietary license. Therefore, the scheme is called dual-licensing scheme, for example, http://www.fsf.org/blogs/rms/selling-exceptions

A dual-licensing scheme, however, can bring loss to the software company. The software company can suffer loss if the number of general public feedback and the number of high-quality copy-lefted free software built upon the software are less than the number of high-quality proprietary products built upon the software and the number of people that are drawn into the proprietary software. Therefore, to be on the safe side, the software company should stick to only sell its software under a copy-left free software license. But, depending on its own research, the software company may be better off with a dual-licensing scheme.