Spot on.
No battery charger (whatever their marketing informations says) is clever enough to spot reduced capacity due to a failed cell or spulphation. Once you've flattened a lead acid battery, you've irredeemably reduced its capacity. No fancy charger will recover this lost capacity - once it's gone, it's gone forever. The charger just charges normally until it's charged to the new reduced capacity and gives you a little green light to say it's done its job (which it has - your knackered battery with its reduced capacity has accepted all the charge it can).
You can often get away with this reduced capacity with no ill effects until the battery is otherwise challenged (lot's of short journeys which don't give the alternator chance to replenish the starting loads, cold weather, the previous in combination with lots of accessories, etc).
The secret to prolonging battery life is to store it charged and on a float charge if left for any length of time (even with no load, batteries self-discharge over time). Lead acid batteries love being fully charged and hate deep discharge - the rule of thumb for a lead acid battery is that you should never discharge it to more than half its capacity - hard to tell on a bike and pretty difficult due to the battery really being smaller than is ideal.
But the really golden rule is don't flatten it. Ever. Once you have, you've stuffed it.
and still holds a charge if I forget to switch the Optimate on 
