What this means is those users who have elected to install updates manually will have 30 days to install Windows 8.1 Update on Windows 8.1 devices; after this 30-day window - and beginning with the May Patch Tuesday, Windows 8.1 user's devices without the update installed will no longer receive security updates.
I don't see how this is a big deal... They will get offered update 1 when they go to check for updates and then they will get offered the rest of their missing updates.
I can see this mattering if you had to manually update to update 1 even if you used auto updates, thus cancelling auto update. But how is this any different for a user who is choosing to manually update? There is always updates you cant get until you install other updates first.