but you will loose all cpu miners and some gpu miners who do not wan't to do software updates untill the last possible moment - some might find swiching to another pool easier than learn about, search, download and configure new software.
In the theory it's true, but the facts suggests otherwise. Our hash rate after getwork removal is equal to hash rate before this. Because benefits of stratum are obvious for all.
Someone will always use the deprecated protocol, while there is a possibility. Many simply due to ignorance or laziness. Thus, the correct policy - to announce the deadline, after which simply remove support for legacy protocols. All will benefit from this, because it will make services and mining software more reliable.
But I'm agree with you, everyone decides for himself what to do.