Hello Moshe
Ah I see. So you have also created a couple of loopbacks on R3 and R4 that exist within Area 0, so even if the physical link goes down, you still have those networks in an active Area 0. Yes, this does improve things, however, if the link fails, you will have a discontiguous Area 0, which itself is also a problem.
It is normal behavior because when you configure a stub area, the ABR advertises itself as the default route only to those OSPF neighbors within the stub area. In your case, Area 102 is the stub area, therefore R3 and R4 will only advertise themselves as a default route via their Gi0/2 interfaces. Area 0 can never be a stub area, since it is the backbone, therefore R3 and R4 will not advertise themselves to each other as the default route. Does that make sense?
I hope this has been helpful!
Laz