This should be a configurable option/filter built in to Greenhopper. There are more use-cases for the chart than just 'calculating velocity', and moreover the duration of a sprint isn't something that's fixed; it goes according to a team's (or company's) preference. If a team is running weekly sprints, you might want 10-12 datapoints to use when calculating a velocity. And if they're running monthly sprints, 7 is probably far too many.
At the end of the day, it's just plain inappropriate (and a clear violation of zero-one-infinity) for Jira/Greenhopper/Jira Agile to be saying "7 datapoints is the correct number, so that's all you get". Jira/Greenhopper/Jira Agile is a tool. It needs to do what its operators tell it; not the other way around.
Hi everyone,

Thank you so much for your votes and comments on this suggestion. We have a few open questions around the design of this feature and would love to hear your feedback on it. We have created a survey to capture the feedback: https://surveys.atlassian.com/jfe/form/SV_8AhloEb2g2MalkF
Thank you again for all your continuous feedback!

Kind regards,
Hanna Sazonava
UX Designer, Jira Server