Ummmm, that 80% means 80% of the people who applied through the AOA system matched, while 20% did not match. I wouldn't call 20% unmatched "impressive" in a good sense.
For
2009
Total DO grads: 3,724 (100%)
Not participating in AOA match: 1,816 (48.8%)
Going military: 203 (5.5%)
Participants in AOA match: 1,794 (includes previously graduated DOs)
Matched: 1,433 (79.9%)
Unmatched: 361 (20.1%)
Compare to the NRMP data:
DO participants in 2009 NRMP match: 2,015
Matched: 1,408 (69.9%)
Unmatched: 607 (30.1%)
US allopathic seniors in 2009 NRMP match: 15,638
Matched: 14,566 (93.1%)
Unmatched: 1,072 (6.9%)
To be fair, the number of DO applicants to the NRMP match has increased by about 30% in the past four years, while the match rate remains ~70%. This growth has outpaced the increase in NRMP residency spots, and thus reflects a greater share going to DO grads. Also, this data does not incorporate the smaller matches (like the SF match).
All that said, at the end of the day, and looking at these numbers, which pool would you rather be in?