The hardware will work but the software won't be turned on until it's ready. For it to become ready it needs to be fed with a higher volume of real time data captured with the full sensor suite. Hence cars with all the hardware present and active must get on the road ASAP, and it's in everyone's interest (including buyers who long for autonomous driving level 5) to get cars out there to collect data.
Right, and if tesla just started including the new hardware and didn't say anything because it wanted to wait until the software was ready, it wouldn't make a difference as people would soon find additional cameras and radars and then the new HW would be reported ad nauseam and Tesla would have to make a official announcement anyway and so really there isn't a better way to do it then just announcing the HW is shipping on all new production cars and the software is soon to follow.
Now compare Tesla's position here to Uber's. Uber has what a few dozen highly equipped test cars puttering around pittsburgh collecting data. Tesla will be churning out onto the roads over 2k of these fully equipped AP 2 cars per week, . Even when no AP is on tesla will still be collecting all this valuable data. And tesla owners tend to be wealthier/better educated, more technie people, e.g. ideal early adapters / beta testers.