Luckily, I could have a chance try both HW-D450 and HW-C450 (2010 model)
After I read a review on Amazon which states that D450 cannot be controlled by Samsung TV's remote (also 2010 model), I decided to purchase HW-C450 instead for the best compatibility as I use TV's remote a lot for using DLNA.
But the seller sent me D450 by mistake, and I could have a chance to try it before I ship it back. As stated in Amazon's user review, soundbar's volume cannot be controlled by either TV's remote (2010 model only) and also universal remote (Time Warner Cable). I could not find a remote code for it and even Samsung customer support ppl acknowledged it. Also for couple of days that I tried, random input change problem (notorious from HW-C450's reviews) occurred once. This was the main reason that I've been waiting for D450 as there were so many reviews complaining about input change problems and other few problems as well.
So I returned D450 and just bought C450 from local store. So far (for couple of weeks), there was no problem with random input changes or anything. I guess the product that I got has the latest manufacturing date or I've been lucky so far.
To compare D450 and C450 (I am not an audiophile), D450 was slightly better than C450 for faux surround effect I guess. Also D450 had 3D surround option which was not existing in C450.
However, as I did not like fake surrounding effect at all, I just used CINEMA sound mode which gave me overall best sound quality in both dialogue and special effects in movies.
So far, I like the soundbar a lot. If not for that compatibility issue, I would have definitely kept the D450 for sure. I do not have the Harmony yet, but maybe Harmony can control D450 since it is the king of universal remotes