Vanguard, the company behind the world’s-biggest emerging markets ETF, cut the price of that fund, VWO, by 10 percent yesterday. It also slashed fees on five other ETFs, saying the cuts reflected asset growth for the funds. All the ETFs were and remain the cheapest in their respective classes.

While Vanguard officials are loath to describe the company’s low-cost strategy as part of a price war, many ETF industry sources say that asset-gathering in the pure beta portion of the market will be fought in large measure on price. The only other firms that have shown the stomach to play the low-price game are Charles Schwab and Scottrade unit FocusShares.

The Vanguard Emerging Markets ETF (NYSEArca: VWO) now costs 0.20 percent, compared with 0.22 percent previously. Coincidentally, VWO's rival behemoth developing markets ETF, the iShares MSCI Emerging Markets Index Fund (NYSEArca: EEM), dropped its expense ratio by 2 basis points as well earlier this year --to 0.67 percent from 0.69 percent previously.

“It relates to our at-cost corporate structure,” John Woerth, head of public relations at Valley Forge, Pa.-based Vanguard, said in a telephone interview about the reason for expense-ratio reductions. “Given the growth of our ETFs over the past year, we’re delivering additional cost savings,” Woerth added.

Woerth said the aggregate savings on VWO amounted to $10 million and to $15 million on all six of the ETFs. VWO had almost about $54.6 billion in assets as of Feb. 28, according to data compiled by IndexUniverse.

VWO's closest competitor in terms of price is the Schwab Emerging Markets Equity ETF (NYSEArca: SCHE), which has an annual expense ratio of 0.25 percent.

The change on VWO’s expense ratio was effective Feb. 28, as were the price cuts on three other ETFs. Those funds and their lowered prices are:

• Vanguard Total World Stock ETF (NYSEArca: VT), 0.22 percent from 0.25 percent
• Vanguard FTSE All-World ex-US ETF (NYSEArca: VEU), 0.18 percent from 0.22 percent
• Vanguard FTSE All-World ex-US Small Cap ETF (NYSEArca: VSS), 0.28 percent from 0.33 percent

The final two fee cuts were effective Feb. 27 and are as follows:

• Vanguard Total International Stock ETF (NYSEArca: VXUS), 0.18 percent from 0.20 percent
• Vanguard High Dividend Yield ETF (NYSEArca: VYM), 0.13 percent from 0.18 percent.