Your statement reads to me as confusing. If the OP had bought in @ $30 and watched the coins plumet to $15 he'd have $5000 worth of coins now. Bitcoin prices can go... anywhere. Back to 30, up to 10000, or down below 1. OP doesn't sound like the patient optimistic type with $10,000 he can have lying around without regards for months or whatever potential time it would take to get back above $30.
Perhaps you bought in around march? In what way would you have made triple? In march prices were about $1 per coin? Let's say that. And prices were $30 per coin around Jun7th right? Difficulty was around 70,000 I believe.
So lets say you bought a mining rig on whenever and got it running march 7th, and you bought some coins on whenever around march 7th as prices were pretty flat until around april.
You could build mining rigs for about 1.7Mhash/$ pretty easily back in march, so let's compare a $10,000 buy:
$10,000 -- 10,000 coins vs 15GHash (bein generous with overheads other than rigs to compare to OPs costs), and use 15¢/kWh like OP, $26.64/day costs.
March 7th: Miner 0BTC $10000Debt , Buyer 10,000BTC $10000 Debt.
2 difficulty changes, both minor, avging to 80k difficulty generates 5,733 bitcoins in a month
April 7th: Miner 5,733BTC $10799Debt, Buyer10,000BTC $10000 Debt.
2 difficulty changes, both reasonable, averaging 90k difficulty generates 5,096 bitcoins in a month
May 7th: Miner 10,829BTC $11598Debt, Buyer10,000BTC $10000 Debt.
Here is where things got crazy, 4 difficulty changes, ending at 400k difficulty. for ease of my lazy brain will calculate whole month at 300k to be generous again. Generating 1528 coins in a month.
June 7th: Miner 12357BTC $12397Debt, Buyer10,000BTC $10000Debt
If the buyer cashes out on June 7th smartly surmising the $30 bubble line, he is still $70,000 behind the miner. If you assume the miner cashed out to cover his costs each month the miner still has 11292 coins on june 7th, putting him $40,000 ahead of the buyer. This is a far cry from making 1/3rd as much. Not to mention even at todays difficulty rate a 15GHash machine produces 125BTC/wk
Your scenario is only true if you assume a miner must cash out immediately the moment he has generated coin all the time. Which doesn't make sense. If you have $ you can just let sit in the market, why couldn't you let your $ sit in easily resalable machines? If you were so finnicky about money that you need to see it recovered INSTANTLY would you really have been able to see bitcoin prices surge up, then make huge drops and not sell off? In the optimum scenario of a terrified miner vs a super bold coin investor maybe your statement makes sense, but otherwise not.
Your scenario relies on perfect information and predicting the market, which no one has and no one can do. "If the buyer cashes out on June 7th smartly surmising the $30 bubble line" that is ludicrous, no one predicted $30 as the bubble line, and being smart has nothing to do with it, you cannot predict it.
Your scenario is only true if you assume a miner must cash out immediately the moment he has generated coin all the time. Which doesn't make sense. If you have $ you can just let sit in the market, why couldn't you let your $ sit in easily resalable machines?
If you are not cashing out immediately you are only trying to predict the market and that it will rise, which is not a given fact by any means.