VMWare are planning to fail
VMWare are currently still popular because they were the market leader. Unfortunately they are driving away partners, customers and consultants at the moment. Existing VCP qualifications must be upgraded before December 31st if we are to avoid taking another course. 4 Months may seem a lot of time, but for a working (and billable) consultant 4 months is very short indeed. Taking a single day off for an exam is bad enough, but taking time off for a course is a slap in the face for those that would pass the exam anyway.
They have also increased prices and made the number of SKUs very confusing while adding no benefit (just like MS and Vista). The partner logon has been mucked about with causing us all to spend 30 minuted fixing our previously working logons (username AND password changed without notice).
Now I've previously pushed VMWare over everything else, and between that and Hyper-V there is still no comparison. Xen on the other hand has come along nicely and now contains all the features most companies need. It also only has 3 editions - free better and best. One of those is free and contains the most used virtualization features. Citrix also gave all of our consultants free training courses, beta software and plenty of information about what's coming up.
To answer the article as to where Citrix get their money, look at their whole product stack. Xen Server is helping them sell a plethora of other software and a foot in the door is better than out in the cold. Provisioning server is genius, and Xen Desktop is easily the best VDI solution while XenApp (Citrix Metaframe Presentation Server Winframe XP yada yada) still presents a great SBC solution which they make plenty of money on.