[Mightypeon]

The point about interesting tactics opened by improved arbalest range is well taken, yet I do have to add something else:

There is another important breakpoint:
At Protection 20, Crossbows do an average damage of 0 (no bonus to the DRN rolls), while Arbalests still do a damage of 4.
Protection 20 is nearly exclusive to Plate units and heavy cavalry.
Many of Ulms mellee troops (everything wearing Blacksteel) have Protection ratings in this area (21 to be exact, meaning that Damage is DRN comparison -1), and are thus "resistant" to Crossbows but not Arbalests, which is also a reason to favor them over the protection 17 troops under most circumstances.
So, while the Arbalest does more damage to Protection 10 troops tangling with Ulms mellee, the crossbow does a bit less damage to those enemies, yet nearly no damage to Ulms own forces. Against enemies engaged in mellee with Ulms national troops, Crossbows are better.
Due to range, and the fact that an Arbalest will propably one shot archers with 10 HP and less than 8 protection, Arbalests are better for targetting archers, but Sappers do this job quite nicely too.

Friendly Fire from Crossbows is further reduced by crossbows beeing 1 more (actually 2 since precision above 10 counts double) precise.
Also, Crossbows are better point blank weapons with a "no deviation range" of 5 squares.
Now, if I had the choice of Sappers with Arbalests or Sappers with Crossbows, I would pick the Arbalests in many cases, and the crossbow in other cases.
But if you add Map Move 2 (which is rare and thus highly usefull for MA Ulm) and the Siege Bonus to the bargain...

Also, in my opinion the gold cost difference (iirc 10 for the arbalest and 14 for the Sappers) exists but both of those troops only cost 1 upkeep. And the lower resource cost on the Sappers allows you to buy more superior Blacksteel heavies for your mellee line.