you said nope... to what exactly? i asked you a total of 5 different questions.
everything i mentioned can affect perceived sharpness. without knowing the exact details (at a minimum everything but the model numbers) it is impossible to tell you why you aren't seeing the same quality.
just because you have HD cable doesnt mean that all channels are in HD. remember also that they refer to hd as either 720p, 720i, 1080i or 1080p. a 720p HD signal will look like crap compared with a 1080p signal displayed in a store.
compare apples to apples instead of apples to oranges as they say.
there is a difference in quality between hdmi cables but the difference is so pathetically small that it isn't worth worrying about. you could go out and buy a $60 monster cable hdmi cable or a $10 rocketfish one and you will not notice a difference. the only case where you might notice a difference is in very long runs of 50ft or more.