After buying Time Warner Cable, Comcast Corp. says, it will authorize spending up to $10 billion more to buy back its own shares on the stock market.

Apple boss Tim Cook said recently that his company plans to spend an extra $30 billion doing the same thing, boosting Apple's total share-buyback authority to $90 billion.

Why do these household-name companies that count tens of millions of Americans as customers plan to pump all that cash into their own stock?

How can they afford to, after funding multibillion-dollar acquisitions, system upgrades, research, marketing projects, and share dividends?

And what does it tell us about supply, demand, pricing, and competition when successful companies pile up that much cash, then spend it like the legendary snake that swallowed its own tail?

"It's a strategy question: You're bringing in all this cash; what do you do with it?" said Robert Costello, president of Costello Asset Management in Huntingdon Valley, which invests $80 million for clients.

At many large companies, buybacks prop up share prices and help prevent fat stock-option grants to corporate executives from "diluting" the value of other investors' shares, Costello said.

Apple and Comcast have been active acquirers of other businesses. But "they can't keep buying everyone they don't own," Costello told me.

Why not invest in creating new business lines, then? "Not too many companies, at that size, are going to build new businesses from scratch," since that would depress their profitability and make them less attractive to investors, he pointed out.

"A boatload of cash is a good problem to have," Costello added.

Don't fat markups and high profits prove a company selling basic goods and services - like smartphones, or Internet access - is uncompetitive and is charging higher profits than a free market would allow?

"Price margin is one way of showing market power," Rutgers Law School antitrust expert Michael Carrier agreed. But simple profitability isn't enough to show a company has gained illegal market power, he added. You have to consider, for example, what is spent setting up networks and developing products. Regulators such as the Pennsylvania Public Utility Commission have set up their own formulas for determining when an electricity or water company is making enough money for its investors - and when it's gouging customers.

"Maybe they don't have enough competition," Costello said of the buyback giants. (Though that's not a problem that will bother too many of his investment clients who own the stocks, he added.)

"But what's the government going to do?" Costello concluded. "They used to regulate [the phone and video businesses]. Then they deregulated. Are they going to re-regulate?"

Not much here

RJMetrics, the Philadelphia-based online-analytics firm, offers a crude but intriguing test for flagging the nation's tech start-up hotbeds: Cofounder Robert J. Moore checked user data for social-group network Meetup, which Moore says has become the "geek elite" online super-community, with 3.7 million members in more than 16,000 tech-themed groups.

His firm found the top U.S. cities for Meetup users, growth, and density are the usual tech and investor hotbeds: San Francisco; New York; Seattle; Washington; Austin, Texas; Boston. But Philadelphia punches way below its weight: the fifth-largest U.S. city ranks only 19th.

Moore, a Glassboro native and Princeton grad, said he's puzzled: He's found the city welcoming enough. Maybe Philly's dominant drug and medical sectors don't Meetup like software workers do, he suggested.