PS3 comes in 160GB and 320GB SKUs and in various bundles with extras like Play TV, different colours, games and PS Move, et al. 

XBox 360-S comes in 4GB, 250GB SKUs and in various bundles with extras like Kinect, game bundles, accessories, et al.

The prices are usually cheaper for the smaller HDD SKUs. In my opinion the 160GB PS3 Slim and the 4GB XBox 360-S offer the best value for money. Bigger HDDs can be bought cheaply online. 

Is the larger HDD plus the 3 or 4 cheap games worth the extra $100 added to package?
If it is a new console for new gamer or a new console to replace an old console.

The extra value added bonuses could be sold separately and make the console cost price even cheaper. An XBox 360 for $100 or a PS3 for $150 sounds like a bargain without the effort of having to sell off the extras and outlay a higher amount of money.

Kinect and PS Moves are in demand and they can attract a good price.

Standalone 250 GB hard drive for Xbox 360 Slim costs 100 bucks on amazon, so no, I think that a bundle is cheaper that buying stuff piece by piece.

Of course, if you're sure you don't need bigger HDD atm, you can just buy a cheaper SKU and get HDD later.
Back in early 2009 I decided to get 360 Elite, simply because Pro was only a bit cheaper than Elite, and 120 GB HDD costed way more than the price diffirence between models. Since I install every game I own, this space is really useful.