Where did this information come from? Are you talking ADR's [ADS's] or underlying Australian or UK shares? According to the Investor Tab on BHP's website the concluded 2004 Capital Management Program, buyback program ended in February 2011. A small off-market buy back was then announced, but ended in April 2011. I find no info about any buy-back for either calendar or fiscal year 2012.
What's bad about eliminating 11 % of shares, raising EPS, supporting share price, increasing dividends to those share remaining? Fewer to share the profits with. BHP has a stated Capital Management and Dividend Policy on their website. Investors who don't like that approach can invest elsewhere. Long and Lovin' it.