Personally, I see them as very similar. The concept is much closer than, say, BJJ and Judo, or Wrestling and no-gi.
If your trying to say they are similar yet different I suppose that is true. It is one of those things where you say, "yeh they are not different yet in this you ______ & this you _____". For me, I think the keyword is control. In no gi the lack of it means you need to control your opponents arm better. In gi, the control is different, you can use their gi aswell as your own to apply pressure & execute techniques. For those who don't know. Differences with grip are: For head region: The back of the neck for no gi/ for gi you can use lapels For mid section: Underhooke & overhooks seem more important with no gi/Lapels can be used again & also wrapping the gi around their body. Lower: no gi you grap their quads & actual feet (I hate that)/ gi you can use trousers. etc etc. That is just my $0.02 with the stuff notice. Gi, you have more offense & has tougher defense, no gi is easier to defend & harder to attack.
Really? I'm still a beginning grappler, but it seemed to me that Judo/Sambo/BJJ were very similar. I remember reading one post on here by a Judo guy saying that sport Sambo is basically a less popular soviet-born Judo. And the Judo I do know seems to be very similar to BJJ without the less dangerous locks/submissions and more emphasis on takedowns with less emphasis on those submissions, and specifically, the guard. On the other hand, one article I read (not a post here) by a BJJ black belt said that something like 60% of your choke/grab/post strategy was unavailable in NoGi grappling and drastically altered.