I have bought (new) and sold 4 cars in the last 8 years, so I'm familiar with taxes paid and losing value. I'm just shocked that BMW has lost so much.
I use Edmunds (trade in) as a good gauge to see how much I could realistically sell it as it was pretty close to what I sold my prior cars. Maybe other regions are different, but in S. Cali the market is pretty saturated.
For example, I bought a G35 sedan that I sold after 1 year of ownership. The money that I lost on the sale was under $5K ($3,500 of it was tax). The average monthly lease payment on the G35 sedan at that time was $400 per month. 12 months x $400 = $4,800 (if I was to lease it).
Just didn't expect that I would lose $1K a year in depreciation on my 2011 coupe. I know that if I keep it long enough, 5 years +, the annual depreciation will even out to some degree. I guess it makes more sense to lease BMWs as I saw some ridiculous incentives (i.e. leasing a 2012 coupe for about $300 a month).