The point is that many BI enterprise solutions are mere data extractor with very little intelligence built into them. That means that people have to download big chunks of data and run models in Excel. No, you won't convince people to move away their models from Excel, but you can/should build an analytical layer on top of your BI warehouse solution so that people will use Excel less. Unfortunately, big BI stuff is very unflexible and building good models (aka: dashboards) can take months or even years. Excel is the de fact answer to that unflexibility, solve that and you will see far less spreadsheets moving around.