I realise the Titan was an example, however when looking at the higher power creatures (thus many with the really strong DR), people also need to take into account preperation. In few "normal" games will you find the Titan (or pitfiend, etc...) wandering in the forest. You'll likely know that you'll be facing this threat and be able to prepare properly. Spellcasters will likely know (if they're high level as well) the opponent will resist most of their spells and prepare buffs instead, preferably the "align weapon" spell and anything else that may help bypass DR.
As an asside, does anyone know exactly how the listing on monsters bypassing DR is explained? I know the specifics is that a monster with DR/x counts as a weapon of x (or from what we see the opposite of x for alignments).... But since stoneskin gives a DR of x/adamantine would that mean a target of this spell attacking (with probably natural weapons) would count as thus?
Plus we shouldn't discount the likelyhood of new magic weapon enhancements. It didn't take WotC long to come up with the wonderful ability of SureStriking in 3.0, a +1 ability that allowed the weapon to strike as a +5 regardless. What's to keep us from assuming that there will be an ability of "Blended Metal" Which will allow the weapon to strike as any special metal or at least one specific metal. Similarily we could see something that lets the weapon simulate an alignment or two (or to channel the user's alignment)?
Finally, its my hope that they change the alignment DR slightly. A demon/Tana'ri who under the preview would have a DR of X/Good, should be changed to X/Good or Lawful, being the two diametrically opposed alignments. This would solve the BloodWar solution a little. A more complicated solution would be to allow the same alignment I proposed (X/G,L) but require a LG weapon to bypass all DR and any weapon that is G or L to bypass half said DR.