True, Docker makes everything much easier. But Docker engine needs a server to run. So learning how to work with servers and goes a long way for software engineers.
One of the main reasons there are many startup founders who dont really care about being entrepreneurs (making money or closing value/profit loop as Daniel says) is a great desire by VC community to profit on the tech startup boom.
Look at the majority of new startup accelerators out there and the message they are transmiting.. The fact is that all these groups are funded by clever investor money to play the numbers game. Simple as that. And in this numbers game majority of scalable startup founders are being left hanging in the air. This creates virtual reality of some sort..
Check out this interview with Steve Blank, he wraps it up nicely http://www.youtube.com/watch?v=TYCE3980kPA
I have nothing against charging fee for your work but hey, you have to make it very clear. Now your site still says its free to use.. and I also believe you clearly are trying to give this impression to potential users. This is not fair.
Side projects are good for you? I think it depends.
Enterpreneurial types in most cases can't specialize (they get bored and demotivated quickly while doing it) but trive while stiching things together and see them work / produce results. This is their motivation and if you are such person and do not get enough of playground at day job you have 2 options, quit or kick off some side projects.
I also admire people who can specialize. Lets call them real engineer types. Only because of them we have all technology things running day to day. But I guess side projects are not such necessity for these guys.
In both cases I was talking about people in software dev space.