If the Malware has reached the kernel it hardly matters if its Limited user or Admin.
However if its a Worm (that spreads across network) then admin priviledge would have come to play.
the Underground economy relies more on these nowadays.The people who write these codes have become more smarter with the freely virus creation tools avialable ,sophisticated and professional.
They write thousands of malwares daily wheres few years back they used to write 10-20 in a day.
Its very tough time for Antivirus industry but they are still able to catch most of them if not all..