An "average full-time web developer" covers a huge number of roles, most of which don't solo end-to-end on applications.

don't forget payroll tax, supplied laptop/desk/electricity/etc, sick leave, annual leave, any skills development, the fact that you're also doing sales (which is probably more than 70K)..

Just because you have 70,000 listed on your annual pay summary - does not in any way mean that's how much your company spends to keep you employed. When you are a freelancer - you take on a lot of those costs yourself.

There are wild variations between what two different "web developers" can produce. As the type of person who is actually interested in programming enough to be hanging out on a site like this, you are probably at the top end of the chart without even realising it. The bottom end is the schmuck clicking around in Dreamweaver, you never see him but he outnumbers you 20 to 1, and he is dragging the salary down to 70k. If you are familiar with statistics, you might say that 70k is the mode but I doubt it is the mean.

Everyone should listen to tptacek, he is absolutely right. It is the value you can deliver, not what your actual cost is. A good web site can be literally worth millions. Deliver the final product, end to end, and you can charge a good proportion of that. 70k is "sitting down money" and most good web devs should not accept anything like that.

Most freelancers who can solo a multi-month .NET or RoR application make more than 75/hr.