Why does IBM suggest one table per database?

I rather new to DB2 though I've been an MS SQL DBA for well over a decade, and I'm having a hard time grasping the concept of table spaces. I've been reading IBM's notes on Table Spaces here - IBM Information Management Software for z/OS Solutions Information Center - but it says something that I find most illogical:

I've written databases with many dozens of tables, and though I'm used to the idea of schema's in MS SQL to keep similar tables organize, but I find it odd that IBM suggests having one table per database. Am I reading this right??? If so this is fundamentally different from every other RDBMS I've worked with. I mean if I need to write a system with 20 or 30 tables then per IBM's 'best practices' I must have 20-30 databases each with a single table space and single table?

Thanks for any info on this or where my logic is flawed. This really has me scratching my head...

Sam