dgl-4500 has been out for a while. Lack of response says the company is turtling and hoping people go away. Their dev cost to fix this is probably higher than the number of routers out there, and it's not worth their time to fix it at this point. It doesn't appear that they can't fix it easily. In fact their easy fixes appear to have made issues worse, complicating and compounding the various issues to the point where the cost to repair is greater than the cost to retain. Since the DGL appears to be a niche market when you compare the overall numbers, and due to the tightened of resources in the down economy some executive probably saw the bottom line and said kill it.
My 1.21 has been getting progressively worse to the point where copying a 300mb file from 1 PC to another on the lan takes 25 minutes. This is the official supported firmware, and it's broken. At this point I've been reading closely the various reviews for other router vendors, doing my homework and replacing it.