Powershell Timer / Stopwatch Accuracy

Finding that the System.Diagnostics.Stopwatch class has what appears to be measurably inaccurate even for a short period of time (i.e. 20 seconds). My process shows a elapsed time of 20.3 + seconds for a process encoded to run 20 seconds:

$elapsed = [System.Diagnostics.Stopwatch]::StartNew()
write-host "Started at $(get-date)"
for ($t=1; $t -le 20; $t++) {
    Write-Host "Elapsed Time: $($elapsed.Elapsed.ToString())"
    sleep 1
    }
write-host "Ended at $(get-date)"
write-host "Total Elapsed Time: $($elapsed.Elapsed.ToString())"

    Started at 02/02/2013 15:08:43
    Elapsed Time: 00:00:00.0329924
    Elapsed Time: 00:00:01.0417435
    Elapsed Time: 00:00:02.0547547
    Elapsed Time: 00:00:03.0689716
    Elapsed Time: 00:00:04.0820497
    Elapsed Time: 00:00:05.0963413
    Elapsed Time: 00:00:06.1113915
    Elapsed Time: 00:00:07.1244044
    Elapsed Time: 00:00:08.1396105
    Elapsed Time: 00:00:09.1528952
    Elapsed Time: 00:00:10.1659905
    Elapsed Time: 00:00:11.1800884
    Elapsed Time: 00:00:12.1940009
    Elapsed Time: 00:00:13.2081824
    Elapsed Time: 00:00:14.2223585
    Elapsed Time: 00:00:15.2375023
    Elapsed Time: 00:00:16.2506360
    Elapsed Time: 00:00:17.2656845
    Elapsed Time: 00:00:18.2790676
    Elapsed Time: 00:00:19.2928700
    Ended at 02/02/2013 15:09:04
    Total Elapsed Time: 00:00:20.3080067

Can this accuracy deviation be expected when using the Stopwatch class in Powershell? It seems that the increase is disproportionate to the time interval (i.e. 10 seconds is disabled by 0.1 and 20 by 0.3). Is my code malfunctioning?