OK, I picked up the SHE3575... Some combination of the decrease in bass and harsher highs & I prefer the 3580s for sure. I burned them in last night & they SEEM to be a bit more mellow. I'm limited to EQ options with iPhone and iPod but the default bass boost setting evens things out a bit and they sound pretty darn good.
I thought the cable packaging was bad on the 3580s with twisty cables which have since straightened out. The packaging on the SHE 3575 is about 10x worse! The skimpy cables above the Y and mic (the cable is thicker on the left to the mic) are so badly pinched out of the package they may break off any time as they are hanging from a thread... very annoying. I initiated a chat session at philips and after exchanging some info I don't think I'll have any difficulty getting them replaced after I fax the ticket number and a copy of the receipt on Monday.
Other thoughts: the tips are softer that the tips on 3580 and work really well. No complaints on the mic & the mic button works for track control on my iPhone4 and iPod touch 2nd gen but not on latest gen shuffle
Also, poking around philips site there are some new heavy duty headphones that look interesting. Hopefully, we'll see them in the US by April: