Wrong. Wrong. Wrong. Developers actually like having hybrid versions (ex. there 32/64 bit applications on Leopard, running simultaneously). IE 64-bit takes 32-bit plugins. The gain you see is rather small, vs the amount of effort. To port from 32 to 64-bit takes tremendous amounts of work, especially for mainstream apps/suites like Office, Adobe CS, iLife, iWork. What do you gain? A few seconds faster launch time. Faster calculations and more memory streams for the >1% people that actually touch upon this every once in awhile.
64-bit calculations do not benefit over 32-bit. Processors are already calculating in 64-bit, but the applications limits it to 32-bit. My MBP addresses 4GB of memory which 32-bit processors can't. But my applications are 32-bit, which limits everything. PowerPoint's new video overlay features won't see a dramatic improvement whilst in 64-bit mode. And Excel is already good enough for most. Improving it to cater to the minority is not a good business model. Apple is a good example. Decades before, they were expensive machines. Nowadays, they are catering to the consumer market. Glossy glass screens, backlit keyboards, multi touch, etc.
A good example of 32-bit being already good enough is CS4 Photoshop. Photoshop is far more powerful and CPU-hungry than the entire suite of Office combined. Photoshop still runs pretty fast. While I see the performance gains in 64-bit, for an Office suite, it's simply not completely-necessary, especially if you want a few seconds faster launch time.