$100/hr is only that much if you bill 40 hrs per week, every week. It does not account for non-billable time, vacation, sick time, etc. You are also taxed higher and have to provide your own benefits. You are taking on higher risk due to the temporary nature of most engagements.

If you're billing $100/hr you're not making bad money, but it's nowhere near equivalent to a $200K W-2 job.