Most of the money to pay others comes from your own upgrade, withdraw fees, upgrade fees, etc. Also, for every day that you're not able to surf the minimum amount of sites for that particular day - you don't get paid. It's your responsibility to remember to take a good 20 minutes or so every single day to earn your pay. Granted, people with a lot of money invested will not be able to forget, many people do.
You're also forgetting that you don't need to put in a penny to start an account. They give you $10 free to start, which you can build up and compound every month into enough money to withdraw, or to continue to compound again. Pyramids require a membership fee. You don't have to put in anything other than your time to earn money from ST. I'll post an example below that another ST member listed, using a completely free $10 account:
Month 1: Account Level = $10.00 Earnings = $3.00 (the best strategy is take this $3.00 and upgrade your account with it so that you will now have a $13.00 account level and from here on out, we will upgrade your account level with your earnings until you have an account level which makes a decent amount of money)
Month 2: Account Level = $13.00 Earnings = $3.90 (earnings is more now because you upgraded your account level from last month's earnings, you still didn't spend $1 of your own money)
Month 3: Account Level = $16.90 Earnings = $5.07
Month 4: Account Level = $21.97 Earnings = $6.59
Month 5: Account Level = $28.56 Earnings = $8.57
Month 6: Account Level = $37.13 Earnings = $11.14
Month 7: Account Level = $48.27 Earnings = $14.78
Month 8: Account Level = $63.05 Earnings = $18.92
Month 9: Account Level = $81.97 Earnings = $24.59
Month 10: Account Level = $106.56 Earnings = $31.97
Month 11: Account Level = $138.53 Earnings = $41.56
Month 12: Account Level = $180.09 Earnings = $54.03
Month 13: Account Level = $234.12 Earnings = $70.24
Month 14: Account Level = $304.36 Earnings = $91.31
Month 15: Account Level = $395.67 Earnings = $118.70
Month 16: Account Level = $514.37 Earnings = $154.31
Month 17: Account Level = $668.68 Earnings = $200.60
Month 18: Account Level = $869.28 Earnings = $260.78
Month 19: Account Level = $1130.06 Earnings = $339.02
Month 20: Account Level = $1469.08 Earnings = $440.72
Month 21: Account Level = $1909.80 Earnings = $572.94
Month 22: Account Level = $2482.74 Earnings = $744.82
Month 23: Account Level = $3227.56 Earnings = $968.27
Month 24: Account Level = $4195.83 Earnings = $1258.75
Month 25: Account Level = $5454.58 Earnings = $1636.37
Month 26: Account Level = $7090.95 Earnings = $2127.29
Month 27: Account Level = $9218.24 Earnings = $2765.47
Month 28: Account Level = $11983.71 Earnings = $3595.11
Month 29: Account Level = $15000.00 Earnings = $4500.00 ($15000.00 account level is the limit they set. You cannot have an account level more than $15000... however, now you just take the earnings of $4500.00 and spend it on whatever you like!)
Month 30: Account Level = $15000.00 Earnings = $4500.00
Month 31: Account Level = $15000.00 Earnings = $4500.00
Month 32: Account Level = $15000.00 Earnings = $4500.00
Month 33: Account Level = $15000.00 Earnings = $4500.00
Month 34: Account Level = $15000.00 Earnings = $4500.00
Month 35: Account Level = $15000.00 Earnings = $4500.00
Month 36: Account Level = $15000.00 Earnings = $4500.00
Maybe I haven't explained it well enough or don't know the economics enough to explain - check out their forums:
http://www.studiotraffic.org/forum/ Look for the threads of people calling it a waste of time or asking how it could survive..