If I'm not mistaken, Steve had said (in the DOTR documentary) that they will already do a 3 months tour instead of the 9-10 months that they've done in the past (the 80's). With bigger production. And the DOD tour was 4 months. Probably they thought that they have to slow down a bit, but then again TBOS tour was 7 months!
But during 2002-2007, the tours were short - GME..'TID (4 moths), DOD (4 months), Early Days (4 months), AMOLAD first leg in 2006 (3 months)... 2007 leg (2 months) with 2 months break in between. And the band had almost 2 full years break in 2001-2002 - a couple of shows in SA in 2001 and the Clive gigs in 2002, which were only 3. But if we see GME.. 'TID tour as first leg of the DOD tour, then it was not short: played a lot of shows in NA and Europe (some big festivals like Download), some SA and Japan shows- the band was very busy during the whole 2003. Let's not forget that they are getting old and all of the band members have family, kids... but after 10+ years since the DOD tour, they tour more (2-3 years) - amazing! It's a natural thing for any band to tour less since their early years/heyday.
Maybe they played only 5 NA shows during the DOD tour, because the previous year they've done a good amount of shows there.
SBIT tour really returned them to the long tours (2 legs in 2 years) - this has to be one of the most successful tours that the band has ever done. Of course, Ed Force One really helped.