If so, from now on nggallery won't be affected by a W3 update ?
NextGen as you probably know has been passed over from a developer to a software house and the latter are heavily changing it.
Until that process is stabilized enough, NextGen will need to be checked at each upgrade even if no W3 TC update comes out in the mean time.
I.e. in the last update, NextGen lost 3 javascript files. Depending on your W3 TC configuration this may mean you have to remove those files from the minification list (else you get some red errors in the admin dashboard). It may get 2-3 new javascript files in the next update, and once again, you'll have to see to add those in W3 TC, despite W3 TC did not get upgraded itself.