No, read the novels dude. Protoss are capable of influencing others' mental capacities. In one of the novels, a Dark Templar (I think it was Xerana in book #2) was being attacked by Aiurian loyalites and struck back by severing their link to the Khala. In the confusion, she cloaked and escaped.
Powerful attack. They can do a lot more than what's shown in-game, according to the novels (which are sponsored by Blizzard and accepted as canon).
Oh, and a Protoss history lesson for ya:
Way back when, like in the days of tribal life for the Protoss (spears as main offense lol), they did share a link with each other. After xel'nagan interference, the Protoss became more selfish and warlike, each tribe convinced of themselves holding the xel'naga's favor. The increasing conflict led the xel'naga to leave, which really set the 'Toss off as every tribe blamed the rest of the race for driving away the xel'naga. The tribes grew apart and eventually all the Protoss lost their communal link, thus beginning the Aeon of Strife.
A very small group of Protoss friends began to tire of the constant war, and began to learn about the world around them. One of them even invented the written language. Exploring together they learned a lot about the xel'naga through discoveries of old temples and establishments, and they set out to reunite their people. One ended up taking the name Khas. Khas accidentally rediscovered the link they once had, and spread it to everyone he could as the Khala, a discipline that pulled all Protoss together and made them almost as one.
Khas became legend, considered a prophet even, as liberator of his people. The Khala persisted, and united all but the small group of Protoss who were afraid that the Khala would rob them of their individuality. The fanatical group of Khalai (the followers of the Khala) rejected the "heretics" and had them originally sentenced to death...but the Protoss commander Adun couldn't bear to murder his brethren and instead secretely arranged for them to go into exile. These exiles became the Dark Templar.