Based on that you only need to have one defense within 50 points, I have a question though.
I know there are reasons when block can't be used, such as against energy/touch based attacks or area of effect attacks. Is there any such restrictions to dodge? I thought it might be that wearing armor reduces your dodge defense, but it doesn't seem to. So, why would you ever choose to build up your block instead of your dodge, unless you just get some nice bonus to your block defense based on your class, etc.?
Actually the ability to touch energy, as with presence extrusion/aura extension allows you to block energy attacks. Blocking Area Attacks is possible without presence extrusion at a -120 penalty (pg 93), however, if you have it you no longer suffer the penalty, even if you don't, you will still want to block an area attack if you are a block-focused character rather than using dodge at -60 because dodge suffers a further penalty of -80 if you are unable to escape the blast radius. Though, I'm not seeing anywhere that says you can't use block against touch based attacks, I am not sure where you got that idea. A touch-based attack must successfully hit and get at least a 10% damage result to take effect just like everything else that triggers resistance.
Anyway, the main advantage of Block over Dodge is, as I've stated above, the ability to block area attacks without penalty provided you have Presence Extrusion or Aura Extension. Another advantage of Block is equipment bonuses, not only do shields give a bonus to block, but the quality of the blocking weapon or shield adds to block as well, while nothing adds to dodge. Furthermore, certain style modules make blocking superior to dodging, such as two-weapon defensive style, and defense from projectiles module. once again, most of this assumes you can stop energy via Aura Extension, but it's such a cheap and easy ability to get, even Weaponmasters should have it.