It amazes me that people good at their trade in western countries do work on oDesk for $50/hr etc.. An example, as someone good at digital marketing, you can usually charge ~$150+ an hour here in the UK for your work. Of course, you don't bill on the hour - but on deliverables, but that's generally how I work out my charges. Estimate how many hours it'll take to do a project, double it, and multiply it up by $XXX (you can then delegate aspects of the work to other employees/remote workers). You'll go higher if you think that there's particularly big ROI involved for the company in the particular case and you can add more value, etc..
$50/hour isn't much money at all, because you don't take into account all the hours you work talking to clients, trying to get clients on board, etc.. A typical contractor is lucky if he can get 3-4 days of billed work a week in + spend the rest looking for new clients. You need a constant flow of contracts coming in.
In the UK it's typical to end up with 4-5 weeks holiday a year. So that leaves 48 working weeks. Assume you're doing well year round and get 7 hours billable work 4 days a week, on $50/hour that's $67,200 a year.
$67k pre-tax, without any of the benefits you'd get doing the same job employed (company car, private health insurance, life insurance, free lunches, pension scheme, etc etc).. It's just not worth it. The same person would do better as an employee, without the stress of having to worry about getting new contracts all the time. That $67k is a best case scenario too, if you imagine you're only getting 3 days work a week, or even worse -- 2. You're talking $50,400 and $33,600 respectively.. $33.6k is barely average salary here in the UK, and $50,400 is only a bit above.
The problem with a highly skilled person in a western country offering their skills on oDesk is that you compete on the same playing field as the Indians and Eastern Europeans, etc who can drastically undercut you. It doesn't make sense for buyers to hire you. However if you approach companies as a contractor in your local area, etc.. You have a massive value add over the Indians and such on oDesk. The company director can come and visit you in your office if you're not doing great, and have a go at you. It's harder for you to escape your duties. You can meet in person and discuss things on a better level, meet the team and get a better idea of the company's culture and what it wants to achieve. There's a greater level of responsibility and better quality relationship built, and that's what the premium is for. All impossible with oDesk.