load average + with no visible load ?

[Laszlo Nagy]

#uptime
 9:06AM  up  6:14, 12 users, load averages: 25.39, 13.19, 9.55

I would think that CPU is under 100% when load=15.58 . But it is not:

#top -S

last pid: 17095;  load averages: 13.26, 11.20,  
8.57                                                                                 
up 0+06:12:25  09:04:27
514 processes: 3 running, 490 sleeping, 1 zombie, 20 waiting
CPU states: 16.1% user,  0.0% nice,  1.8% system,  0.0% interrupt, 82.1% 
idle
Mem: 1406M Active, 272M Inact, 247M Wired, 70M Cache, 112M Buf, 8380K Free
Swap: 4096M Total, 4096M Free

  PID USERNAME    THR PRI NICE   SIZE    RES STATE  C   TIME   WCPU COMMAND
   11 root          1 171   52     0K     8K RUN    0 214:21 43.70% 
idle: cpu0
   10 root          1 171   52     0K     8K RUN    1 282:08 34.28% 
idle: cpu1
   21 root          1 -68 -187     0K     8K WAIT   1   2:15  2.05% 
irq19: myk0 uhci3
16480 timea         1  97    0 34376K 17628K select 0   0:03  1.81% 
wnck-applet
14813 kornel        1  96    0 34376K 27384K select 0   0:20  1.12% skype
17095 root          1  96    0  3104K  2324K CPU1   1   0:00  1.00% top
16443 timea         1  96    0 17304K 12560K select 1   0:03  0.98% metacity
   12 root          1 -44 -163     0K     8K WAIT   1   1:21  0.88% 
swi1: net
16550 timea         1  97    0 41760K 37284K select 0   0:15  0.73% wish8.4
 2317 zsolt         1  96    0 29680K 22344K select 1   3:13  0.59% skype
 3450 szgabor       1  96    0 28344K 21484K select 1   2:56  0.49% skype

The most strange is that "last pid" is almost constant, about 1 process 
started per second.

So how it is possible that "top -S" tells "82% idle" but "load" tells 
15.58 ?

Thanks,

   Laszlo