Vista security credentials tarnished in malware survey

"[Vista]has been hailed by Microsoft as the most secure version of Windows to date. However, recent research conducted with statistics from over 1.4 million computers within the ThreatFire community has shown that Windows Vista is more susceptible to malware than the eight year old Windows 2000
Interesting but i'd like to know how, is it just more malware is written for XP?

Vista is only 37 per cent more secure than Windows XP

Is 37 % better not a significant improvement?