Funny they mention "price/performance" ratios...the rate of depreciation we've seen in the last year on the E60 M5 is nothing short of phenomenal, and something similar has happened with Mercs, Porsches, et al. A 2008 M5 with an MSRP of ~$95,000 can be had with low mileage (say 10k miles) for about $35-40,000 off that list price. Dealers can't give away high end cars in this market. One example is to go to eBay, 911s, sort on model year and just look at the shear quantity of 911s on the market from 2009 through 2007 models. Dealers are even taking big discounts off ordered 2009 cars at the moment. January was a horrendous month for German automakers in their home market and world market.
When you can wait 6-7 months, buy a car with 10k miles and save the price of a new 135i in the process, it's hard to imagine anyone of any means simply wanting to plunk down cash for a new one.
If you've never driven an E60 M5 with SMGIII, take it off your wish list imo. It is stellar on the track or when wringing it out to the max, but everyday driving is a pia. Reliability has been horrible too. More E60 M5s have been towed back to dealers than any other car BMWNA has ever imported as a percent of that model sold (my opinion, but try to come up with any other model that beat this one in that regard).

Perhaps one more reason that 2006 models can be had in the high 30k range now as end of warranty periods approach or have passed for them.