I'm pretty sure that Sage doesn't wonder about why sales of their other ERP lines are down and ERP X3 is growing. But just in case. Almost all Sage marketing points users at ERP X3. What will that marketing look like next year? Will they get more desperate and run migration incentives like they used to do for 500?
http://blog.sageerpsolutions.com/is-it-time-for-midmarket-firms-to-switch-erp-systems/