Not even that's the case. Wikipedia blocks shared IPs. They even blocked the National Library of Scotland which has an official Wikipedian.

Then use a different IP or register an account?

Almost anyone can edit it though they seem to have blocked Larry Sanger the co-founder for being a pain.

	▲	nephihaha 5 hours ago \| parent [-]
		Most of the IPs are used are blocked before they even start. If you do get in there, an editor without a clue will challenge your edits even if he (nearly always a "he") knows nothing about the given subject.