If in the vSphere Client you only see real-time metrics of the last hour for any given counter, then no, vCenter does not store these metrics.
I'm not sure if VMware incorporated that into a later 4.1 Update too. First, check the statistics collection level in the vSphere Client under Administration->vCenter Server Settings->Statistics
Download the LevelMappingUtility.zip file from http://kb.vmware.com/kb/2009532
Connect to your vCenter in PowerCLI and execute the following:
Import-Module D:\VMware.VimAutomation.PowerCliExtensions.CounterLevelMapping.psm1
Get-PxCounterLevelMapping | ? {$_.Name -match "datastore.number(Read|Write)Averaged.average" }
Post the output. The PerDeviceLevel number for these metrics is probably higher than the statistics collection level specified in the vCenter settings, meaning historical data won't be stored at all.