That sounds like a very dangerous opinion to present as if it were a fact.
Is it not more a matter of whether a piece of software is a "derivative" of the GPL software?
Looks like even the FSF does not have a clear black&white answer to this question: http://www.gnu.org/licenses/gpl-faq.html#MereAggregation: "if the semantics of the communication are intimate enough, exchanging complex internal data structures, that too could be a basis to consider the two parts as combined into a larger program"
I remember the mysql guys used to claim that any software connecting to a mysql server would be "infected" with GPL, at least if it was written to depend on the official mysql client libraries, even if the software in question didn't actually copy a single character from any mysql distributions. (?)