I think it makes more sense for them financially.
IEMs generally don't break down in 1 year, the cables do.
By not providing replaceable cables, they will be able to get more sales theoritically.
Guy A buys IEM in Jan 08
Cable gave way in Mar 09
Guy A has no choice but to buy a brand new pair even though the drivers are still functioning.
guy goes and buys a competitors product
guy loves new IEM's and tells all his friends how much better they are than the UE set he used to have with their crappy cables