For Cactus, it is very important that the licence is not standard GPL, as this would make it impossible to use standard Cactus thorns with arbitrary other licences. Cactus needs to be open, and the GPL places too tight a restriction on codes that use Cactus. Of course, this hold only for the standard Cactus thorns (the thorns in arrangements with names starting with "Cactus"); any thorns developed by others can of course be released (or not) under any licence they choose.
The original formulation of the Cactus thorns' licence was somewhat misleading; I believe it used the standard GPL text, and then added a clause that using such a thorn in an application was also allowed. We later noticed that this is essentially the content of the LGPL, and thus changed all Cactus thorns to be released under the LGPL. This policy still stands. If we missed the licence text in a thorn, it should be corrected. If a new thorn was added with GPL as licence, then this needs to be discussed, and either the licence changed or the thorn be moved to an auxiliary arrangement (i.e. not be part of standard Cactus any more).
-erik