The answer is simple:
1. Price - their pricing is inline with other US-based sources.
2. Service - all APC projects seem to have top-priority, and they deliver in the formats we need (Framemaker and hi-res PDFs).
3. Dependability - they are the only source I am aware of, that will take existing files - and work from a mark-up - and only charge for the delta change. Companies that keep a database (like TRADOS), charge for reuse (exact matches = 20%, fuzzy matches up to 35%). Thus, you are in a constant cycle of paying for the same translations. NOW doesn't do that.
4. When NOW quotes a price, it usually includes handling/coordinating/implementing ALL review cycles/comments. Other translation companies charge for each change cycle.
5. NOW also handles translations for Creative Services (packaging) - and they always compare the manual to the packaging - to make sure we are consistent - again, no charge.
6. Zero-defects. In 5 years, we have never had manuals flagged to be in error, once they've gone to press.
7. Prior bad translations. I did use a local company (don't remember the name) a few times. They were expensive, slow to respond, slow to deliver, and didn't seem to want to work with such small files.