[drgondog]

A couple of factors were different.
First the Japanese really didn't have fighters fast enough or high altitude capability to really threaten the B-29 daylight ops until the Shiden and Raiden fighters came into production.

When the B-29's went low as Curtis LeMay decided to do in March 1945, he did so for five reasons:
1. The Japanese had neither night fighters nor adequate radar directed anti-aircraft
2. Much of Japanese industry was scattered/distributed within the cities and surrounded by wood dwellings and very susceptible to fire
3. The B-29's could take bigger loads when they weren't required to climb to 25-30,000 feet.
4. LeMay did not believe that the Fire defense capabilities were adequate to control fire raids.
5. Until the Battle of Iwo Jima was over (March 26,1945), the USAAF did not have an adequate capability to support P-51/P-47 escorts over Japan in daylight.

The truly amazing aspect of B-29 operations were:
1. They were relatively ineffective at high altitude in context of precision attacks despite being the most advanced bomber in the world
2. The guy that decided to 'go low' was the very same guy who was the key leader in the development of 8th AF combat formation structure, lead crew doctrine to improve day to day performance, and the mandate to let the lead crews take control during the bomb run(i.e not take evasive action to improve Norden performance).. in a very different 'hostile' environment defended by the Luftwaffe. LeMay truly 'thought out of the box'
3. The B-29's virtually wiped out Japanese industry doing low level attacks at night..
4. With the advent of fighter escort from Iwo, the B-29's during daylight ops dropped to 20-25K range and improved daylight results with HE, when HE was required.

Interesting how the Luftwaffe and JAF (Navy and Army) had serious blind spots that cost them dearly. The GAF didn't believe and never reall developed Heavy Bombers. The JAF didn't focus on high altitude performance and stuck with the Zero too long.

The USAAF wasn't well prepared either and didn't develop a long range escort by design until reality over Europe reared its ugly head (the P-38 was originally designed as an Interceptor, and really wasn't effective as an escort until dive brakes were factory installed on the P-38J)