I agree with both of the above. It's a surprise because it's not what phone contact lists have traditionally done.

In particular, some other mobile phones let you add and remove IM contact information from their main contact list, but that doesn't affect the server list. That's because it's no different from adding and removing email addresses and phone numbers.

A lot of people even like to maintain different lists on their phone then, say, their computer address book or paper address book of all known contacts.

I expect people who are used to syncing their phone contacts with their big database on Google or on their main computer, and who always aim to have One Big List(tm) on all devices, will not be as surprised.

But they might still be surprised, if they're not used to thinking the IM client way.

After all, if you delete info and then sync, often deletions are synced around too. That said, you usually have some control over this - whether it's dialogues at sync time saying "do you want to delete the following contacts removed from $DEV1 and still present on $DEV2?", or an option to sync in one direction only.

So even regular syncers can correct their mistakes that way.

A lot of people don't sync their phone contact list regularly with other systems. They just maintain the list manually, or bluetooth entries around. They're not expecting deletions to propagate.

Culture clash, I guess, between the way people maintain phone numbers on their phones (and have done forever), and the way IM clients keep a single list on the server.

Well, apart from the expectations difference, there may be a technical surprise which is different from both traditional phone contacts and IM client behaviour:

Judging from the OP's report: "Delete all contacts" deletes contacts that have never been synced onto the phone. That's not even like an IM client, where you can at least see who you're about to delete.