The Steelers D-Line to be a strength or weakness going into the season?

Although everyone was surprised that the Steelers didn't draft an O-Linemen early (Although justifiably so), I was also shocked that they didn't try and add some youth and depth to that D-Line.

Casey Hampton although still better than 95% of the DT's in the league is getting more and more overweight and can barely play a full game anymore. He looked gassed a lot more this past season and I don't think he can be an every down DT if he keeps going down this path.

Aaron Smith, is highly under-rated but can he stay healthy?

The rest of your D-Line is nothing special. Nick Eason and Travis Kirschke are just wavier wire fillers. Brett Keisel is good at times but overall just average.

Also could someone let me in on why Tomlin keeps neglecting the trenches?