Not sure if it's just me, but I had absolutely no trouble going through the checkout process and just finished installing several of the apps. I was never asked for a serial number for Photoshop - it seems to be baked in if you install through their installer and log in with your Adobe ID. (Also, paying $30 per month vs $1900+ up front seems to be a hell of a deal.)
Are you buying new or upgrading? Checking their website the upgrade is only $525. As they only come out with a new version about once every 2 years that. $525 to upgrade vs $720 for a 2 year subscription.
Even if you were purchasing new it's still cheaper to pay outright.
6 years at $30 a month for the first year + $50 for the next 5 is $3360
1900 + 2 upgrades at 525 is $2950