Steven Sinofsky, President of Microsoft's Windows Division has denied any link between Windows 7 and reported battery issues of various laptops. In his recent blog post he added that Windows 7 has better battery management system and those reported issues may have been in need of a battery replacement, which the previous Windows OS (XP or Vista) did not report.
There were approximately 20 known cases on Microsoft Support website which Microsoft investigated and now have denied the involvement of Windows 7 in this issue.
Steven also mentioned in his blog that "Windows 7 is correctly warning batteries that are in fact failing and Windows 7 is neither incorrectly reporting on battery status nor in any way whatsoever causing batteries to reach this state. In every case we have been able to identify the battery being reported on was in fact in need of recommended replacement."
He later on added that Windows does not directly obtain battery information from the battery but from system BIOS, which is basically a read-only information. Based on the analytical tools added in Windows 7, the true state of battery is displayed.
I am not sure about the people who did face the issue, but I have been using Windows 7 on my 2 year old HP and the battery life actually improved. Then again, there has to be a very significant number of cases to be reported to actually establish a link between an OS and battery life reporting.