This was just a missing CSS rule. The class name has actually been applied to the row. Look at the DOM in firebug - you'll be able to add the rule yourself.
It has been fixed for the next release though, and there will be a default CSS rule for the appearance of alternate rows.
I also think that some known or easy bugfixes have not found their way into the final release
really no offence, only my personal hint
but I think the Ext Team should improve its bug management processes a bit;
I think stabilising may be just as important as adding new features to the library
I think a known_issues.txt would also be very useful with each release
so that app developers could be prepared for known issues
and also not to report the same issues on forums over-and-over again
however I think Ext is the best and most useful JS library out there today
thanks for the developers!
I also was not seeing it working, until I moved my browser window from my internal LCD display on my laptop to my external LCD. There I could see that the rows were indeed striped! My contrast on my internal LCD display apparently needs to be adjusted!