That's great, except that it is wrong on all points that show a difference.
First off, all tortoises are turtles, as a few real live biologists have stated already, go look up "turtle" in Wikipedia to see why.
Second, some aquatic turtles (i.e. not tortoises) live in water, yet don't have webbed feet and have highly domed shells. Many species of box turtles are great examples.
Third, large sea turtles can live in excess of 150 years, just like large land tortoises. Small tortoises may live less than 20 years, just like all small turtles.
Fourth, that nesting behavior is not true for all aquatic turtles, particularly freshwater turtles (like the box turtle mentioned above).
Fifth, aquatic turtles are found all over the world, not just Africa and America (in fact, so many live in the ocean and migrate vast distances that the idea is ludicrous).
Last, I don't really understand how turtles can be in the same family as tortoises, but not the same class, and a quick Wikipedia check shows that the link is, once again, incorrect. Testudines is in the Reptilia class, and all turtles and tortoises belong to the family Testudines.
Even better, testudinoidea, the superfamily of which tortoises (testudinidae) are members, includes three families of aquatic turtles. Also, there are a number of non-aquatic turtles that are not tortoises, like the desert box turtle (and a great number of species of box turtle, actually), which belongs to the emydidae family, not the testudinidae family nor the testudinoidea superfamily.
In short, all tortoises are land turtles, but not all land turtles are tortoises.
The turtle depicted in the comic looks a hell of a lot like the common box turtle, which is a popular pet, and also happens to be a member of the emydidae family, not the testudinoidea (tortoise) family.
Again, noticed something else wrong: the nesting behavior of the Tortoise is exactly what is described for Turtle - 90-120 days in incubation, after which a completely solitary life. Tortoises never return to a burrow with their mother. As far as I can find there is no species of turtle which cares for its young.