Yes, it is.
1) Smaller, faster loading pages.
2) Quicker and easier to maintain.
4) All standards compliant User Agents can read and understand your pages.
5) You can put the content in your code in whichever order you want, which has SEO advantages.
6) Multiple stylesheets allow you to present the same pages in different ways (as opposed to writing new pages).
All in all, a huge amount of time and money saved.
A very good business decision.
The Semantic Argument:
Some people will always recommend using tables to lay out pages - possibly because they weren't around when this technique was first used as a hack and thus, to their mind, it isn't a hack - but using tables, makes your html document a two-dimensional graphics tablet. And it isn't. It's a document containing marked-up elements.
You wouldn't position elements around the page using unordered lists, would you? No. So why use tables?