You can do something like this.
Note that this might take a bit of time, depending also on the number of events you keep in the DB.
$start = (Get-Date).AddMonths(-12)
$events = Get-VIEvent -Start $start -MaxSamples ([int]::MaxValue)
$events | where{$_ -is [VMware.Vim.VmCreatedEvent] -or $_ -is [VMware.Vim.VmRemovedEvent]} |
Group-Object -Property {$_.GetType()} | %{
New-Object PSObject -Property @{
Action = $_.Name.TrimStart('VMware.VimAutomation.Vm').TrimEnd('Event')
Number = $_.Group.Count
}
}