First let us look at the numbers:
Dwayne Cherrington - 6'2", 345-pound rookie
Armond Armstead - 6'5", 300 pounds
2013: $405,000, fully guaranteed
2014 $495,000, with $250,000 guaranteed
2015: $585,000, with no guarantees
Marcus Forston - 6'3", 305 pounds
Cory Grissom - 6'1", 310-pound rookie
Signing bonus: $4,000
Base salary guarantee: $4,000
Total guarantee: $8,000
To my knowledge an actual long-term contract has not been negotiated yet with Grissom
Both Love (6'1", 305 pounds) and Deaderick (6'4", 305 pounds) were entering the final year of their contracts:
Love's salary would have been $750,000 (total cap hit of around 1.1 million).
Deaderick's salary would have been $630,000.
Obviously the other four players noted above, not only are signed for less, but they are signed to long-term deals, where as both Deaderick and Love would have been FAs after the 2013 season.
More than likely, even if one of them had made the roster this year, they wouldn't have seen much playing time (with the likes of Tommy Kelly and others ahead of them on the depth chart) and then they would have been looking for a pay raise (peddling themselves to every other NFL team) as soon as the season was over.
Speaking of Tommy Kelly, he is 6'6", 325 pounds, and signed a two-year deal:
Signing bonus: $1M
2013 base salary: $950,000
2013 roster bonus: $500,000
2014 base salary: $1,950,000
2014 roster bonus: $500,000
Kelly is pretty much a lock to make the roster in 2013 at the least, he is a solid veteran that I expect will have no issues at all with towing the line and being a professional.
Now, let us take a little jaunt down memory lane, shall we?
The Patriots went into training camp in 2011 with Marcus Stroud (signed after the Bills waived him, he never played a game for the Patriots and retired before the season began); Ty Warren (who had been one of the walking wounded for two seasons, and hadn't played solid football for the Patriots in a long while).
Plus Mike Wright (who in 2010 had suffered one of the worst concussions I had ever heard about, six months after the concussion that landed him on IR he was still having headaches, and having trouble with bright light); and Gerard Warren (who was very long in the tooth, and had no tread left on his tires)...
The depth players, late draft picks and UDFAs were Kyle Love, Brandon Deaderick, and Myron Pryor guys that might not have even made the roster if not for the fact that those four guys were off the team or IRed by the end of week 1.
The Patriots had also drafted Ron Brace in the 2nd round, but we know that didn't exactly work out for them.
The Patriots, realizing they had a problem early in 2011's training camp, made a trade for Albert Haynesworth, in addition to their other losses, Deaderick and Pryor were starting the season on PUP, so they tolerated Haynesworth until they got Deaderick and Pryor back from PUP near mid-season, and then they dumped him.
In 2012, they still did not bring any big names in for the defensive tackle position, not in the draft or free agency... though they did add Marcus Forston, Justin Francis, Trevor Scott and Chandler Jones, shoring up the defensive end positions.
Pryor, Love and Deaderick had the opportunity to excel in 2012, to improve and step up, but by all accounts they merely treaded water. Some would say Love took a noticeable step back and had been supplanted by Deaderick by season's end. So if Deaderick was released, who was performing on the field even better than Love last season, what chance did Love really have?
The Patriots simply moved forward to conclude things with Love and Deaderick, the end result was highly-probable to happen anyway, before the season ever began.
Look at who is still on the roster at the DT position, and consider this is far more of a 4-3 defense now than a 3-4. And that means instead of playing three DTs regularly, they will only be putting two, and sometimes only one, out there... considering that, it's obvious they still have plenty of depth at the position heading into camp.