Shinji Kagawa, signed for just $300,000 from the Japanese second division, was sold to Manchester United for $17 million, while Sahin joined Real Madrid for $12.8 million.
"Obviously (Dortmund and Bayern) have the power and the money to buy the best players as Bayern has done again; they've signed Götze for £37 million, and you know, the rich get richer, and that's just the way that football works," said Hargreaves.
"People can argue that's not fair, but they paid a lot of money to Dortmund -- and they can invest that money in younger players."
In England, the Premier League has taken a laissez-faire approach to regulating clubs' finances.
Alongside huge television deals -- the latest of which could see a record £5.5 billion ($8.3 billion) windfall in broadcasting income -- extraordinarily wealthy owners such as Chelsea's Roman Abramovich and Sheikh Mansour at Manchester City have been allowed to spend big for success.
But the model in Germany is very different.
Under the league's "50+1" rule, Bundesliga clubs must be controlled by their members -- with at least 50% of shares, plus one, in their hands.
This means a club cannot be taken over by private investors. At the last vote on changing this rule, back in 2009, only Hannover 96 voted to scrap it.
The German system is geared towards preventing the influence of a rich benefactor from skewing the competition, but some argue that it will only serve to perpetuate the status quo.
Hannover has now won concessions in its attempt to change the "50+1" rule, and these will allow sponsors with a long-term relationship with a club -- more than 20 years -- to take a stake in it.
However club fans are already protesting about these changes, perhaps anxious at the advantage such a move might give their rivals.
"The next five years will be interesting," said Dykes. "The rules have had exceptions to allow for the different ownership structures of teams like Bayer Leverkusen and Vfl Wolfsburg, but Hannover has argued that this leaves them at a disadvantage, and you can see why."
But how is a booming Bundesliga affecting German football further down the feeding chain?
In the former East Germany, far from the country's football powerbase, one lowly team's fortunes are being transformed by Austrian soft drink company Red Bull's takeover.
In 2009, Rasen Ballsport Leipzig (better known as RB Leipzig) became the fourth club in Red Bull's football portfolio, alongside Red Bull Salzburg of Austria, Red Bull Brasil, and the New York Red Bulls of the American MLS.
Formerly known as SSV Markranstädt, league regulations prevent the club using the Red Bull brand in its name, so it settled on RB Leipzig instead; but there is no ambiguity over the power driving it forward, with a reported planned $128 million investment to take the club to the Bundesliga by 2017.
After promotion in its first season, followed by two years in German football's fourth tier, its plans look to be on track as the club prepares to contest the playoffs for another promotion in June.
The club's stadium, the impressive 45,000 capacity Red Bull Arena, is certainly ready.
"We accept this rule," said RB Liepzig's managing director Ulrich Wolter, referring to the "50+1" rule.
"The intention of the rule is to secure the league's integrity against short-term investment, I think everyone understands that."
However, Wolter is frustrated at the resistance to RB Leipzig's owners.
"Red Bull is not a Russian oligarch, or an Arabian sheikh," he said. "We've shown elsewhere that we're about a strong, sustainable investment and commitment.
"Why is our way the wrong way? What is the difference between our approach and a club with 50 different sponsors delivering the same thing?"
Even so RB Leipzig's new investors have encountered resistance.
The pitch at its former stadium was attacked with weed killer not long after the takeover, and fans of other clubs can be less than welcoming.