For the centre backs, it's kind of subjective to only nominate Terry and Rio as the best. Rio did many mistakes for the past few seasons, but yet still an undroppable player for England, just because he cost a lot. Terry wasn't even an England squad regular two seasons ago, till Sol Campbell lost his placing at Arsenal. Not to forget, there was Anthony Gardner, Ledley King and even Wes Brown before Terry was even considered. During that time, Chelsea was just another team fighting for fourth place with Liverpool, and Terry was already impressive. Moreover, Carragher hardly get his chance.
It isn't that only Rio is experienced, but don't forget that Vidic is 26 now, with reasonable experience whereas Agger is only about 21. This is Agger's first real season, some tackles are raw and decisions are bad. Carragher is the only one who is organizing the defence and shouting for instructions. You can always see him instructing Agger as well as the fullbacks all the time.
Sissoko is never a copy of Makalele, I'd take that as a compliment if you do say that. Liverpool will be in a better position if Momo is as intelligent as Claude. Claude is a defensive midfielder who stops opposition from attacking with his dirty work. That's all Sissoko does, but what makes Makalele special is that he distributes passes well too, his decisions are always good which is useful. What Momo does is just tackling and distributes bad passes which is useless. That's why you only see him distributing short passes earlier in the season. Not to forget that, he was injured for quite a while during this season. Mascherano is still pretty lenient with his tackles but I gotta admit that he is still a class player.
If the rotation policy affects the team's fluency in attacking, how do you explain Valencia when Rafa Benitez was there? How do you explain our fluency against teams like ManUtd and Chelsea? Most teams in Europe rotate players all the time, even Barca and Real Madrid just to prevent fatigueness of the players. Rafa had this idea even when he was at Valencia, it won them 2 La Liga titles in 3 seasons, 1 Uefa Cup. Furthermore, most of these passings and tactical jobs are done during training sessions. I can't deny that rotation policy may be one of the factors which made us poor while attacking, but there're still other factors like lack of creativity and consistency. A lot of players in Liverpool are in their first season such as Mark Gonzalez, Jermaine Pennant, Kuyt, Bellamy...etc, it is never easy to adapt into a new team, moreover...a few of them came from other countries or continents. These factors contribute more problems to the team when it comes to attacking.
If the number of goals is one of the factor why he isn't nominated, why is Rooney even nominated every season? He didn't score that much either, maybe more than Berbatov, but to compare to a player in Tottenham and a player in Man Utd? Rooney obviously get better services from Man Utd than the Spurs. How many goals have Rooney scored when he was in Everton? I'd see him replacing Gerrard at least. I rather not mention any players other than Gerrard as it might trigger some sensitivity here.