Europa is a lot further away than Mars [1]. Every extra 4600 m/s of delta V in the mission means another factor of e in the ratio of initial to payload mass. At least until we develop better high efficiency rockets.
In practice, the ΔV differences are actually way smaller than that chart suggests. Those figures are for direct transfers (per the legend). But if you allow indirect trajectories with gravity assists [0], that makes things drastically cheaper. To intercept Jupiter, you can steal much of the needed ΔV from flybys of the inner planets (at the tradeoff of time, waiting to go around the sun multiple times). And maneuvering within Jupiter's gravity well can be practically free, by flybys of the Galilean moons. The map tells you 8,890 m/s to intercept Europa, which would be horrifying, but none of that actually needs to be propulsion.
Keep in mind, for a human mission, you want to minimize time, rather than deltaV. Gravity assists will take a lot of time, as you spend a lot of time waiting for the encounter.
Furthermore, that chart is likely computed via a direct Hohmann transfer, which is one of the most efficient transfer maneuvers available. It also will take a lot longer.
For practical human travel to destinations farther way, you need to perform the so called "star wars maneuver", which is going essentially from A to B in a more or less straight line, which will cost a LOT of delta V.
> Keep in mind, for a human mission, you want to minimize time, rather than deltaV. Gravity assists will take a lot of time, as you spend a lot of time waiting for the encounter.
True, but we could throw the big ship with all the supplies into a flight path that gains a lot of momentum around the inner planets and intercept it with a much smaller craft only loaded with enough fuel to get the astronauts to the transit ship (and back, if necessary).
[1] http://i.imgur.com/AAGJvD1.png