Xilinx want to sell chips. Getting cheap devkits available helps this, whether they make them themselves or fund third parties to do it makes little difference - I can't see how this is any way underhand.. In practice, third parties can often do a better job as they are typically smaller companies more in touch with the needs of lower-end users, and are more geared up to manufacturing than chip making companies. Any third party making devkits independendtly of the manufacturer knows that there is always a risk of the manufacturer undercutting them when they decide to do a sales push/promotion etc. Any company whos survival depends on selling devkits for a single chip manufacturer's product is on shaky ground unless they have a very good relationship with the manufacturer.