Tables are good for some things, for others not so much. Do whatever works for you and ignore the pundits stuck in the 2005 "markup quality ftw" mentality.
SEO on a site with tables isn't going to penalise you that much therefore it must be that these SEM marketers are happier building them with tables.
Web devs worry about technical deliverables (e.g. does the site load quickly, can the client edit articles easily, will that affect how print-versions will look like, etc).
SEM guys worry about campaigns, analytics, etc (e.g. did users coming from a magazine ad convert more than a users from a google search, how often did users dismiss a satisfaction survey call to action, etc)
With that being said, markup deliverables can be quite elaborate. Start-ups can, to a cetain extent, do whatever they want with their layouts. When you deal with clients who expect code as deliverables, on the other hand, you may run into pixel-precision freaks, things needing to be quick for other devs to maintain, and other not-entirely-technical caveats that make tables less attractive than CSS-P (or vice-versa).
But are there any advantages - is it easier to design if the site doesn't use complex tables? There really can't be any advantage to download speed - as browsers are likely to render tables slightly slower.