Actually I just did a quick check on if the Memory Usage data on both the Activity Monitor and iStat Menus Memory Usage Bar is it the same ? And shockingly the difference between the two is huge (Check the attached Screenshot) Now this makes me think that iStat Menus which is like touted as one of the cuts have APPS by almost tech sites, is it worth having in your Menu Bar or not ? The Black one is iStat Menus and the White is from Activity Monitor. Any comments ?
If you look in Activity Monitor you will see the main Safari process and also a separate process for each page (tab) Safari has open. For example look on there are icloud.com with 159MB used. If you add those all up, it looks like it comes out to the total shown by iStat menus. It appears iStat menus does not show the individual tabs and just adds them up to one, Safari entry.