In life, anything is easy ... if you know how to do it.
The fact is most folks pursuing Sun certifications are already professional (that is working) developers who want certification for career advancement. Generally, they (like me) want (or need) to focus in specific areas and details they dont often use in their jobs or didnt learn thoroughly when they got started. So taking two or three months to prepare and passing the test doesnt prove its 'easy' rather it indicates that they know the subject.
PS: Brain surgery and rocket science are 'easy' for those who know those fields well. Doug Crockford, the discoverer of JSON, suggests that computer programming is the most difficult thing that people do. While I'm not sure he's right it is an interesting observation.