CaseCommentsComponent.component

<apex:component controller="CaseCommentsComponentController" selfClosing="true">
  <apex:attribute name="accountId" description="The ID of the Account to reference" type="Id" required="false" assignTo="{!theAccountId}"></apex:attribute>
  <apex:pageBlock>
    <apex:pageBlockSection>
      <apex:pageBlockTable value="{!comments}" var="c">
        <apex:column value="{!c.Parent.CaseNumber}" />
        <apex:column value="{!c.Parent.Subject}" />
        <apex:column value="{!c.CommentBody}" />
      </apex:pageBlockTable>
    </apex:pageBlockSection>
  </apex:pageBlock>
</apex:component>

CaseCommentsComponentController.cls

public with sharing class CaseCommentsComponentController {
    public CaseCommentsComponentController() {}

    public Id theAccountId { get; set; }

    public List<CaseComment> comments {
        get {
            if (comments == null) {
                comments = new List<CaseComment>();

                Set<Id> caseIds = new Set<Id>();
                for (CaseComment cc : [SELECT Id, ParentId, Parent.CaseNumber, Parent.Subject, CommentBody, CreatedDate 
                                       FROM CaseComment 
                                       WHERE ParentId IN (SELECT Id FROM Case WHERE AccountId = :theAccountId) 
                                       ORDER BY ParentId ASC, CreatedDate DESC]) {
                    if (!caseIds.contains(cc.ParentId)) {
                        caseIds.add(cc.ParentId);
                        comments.add(cc);
                    }
                }
            }

            return comments;
        }
        private set;
    }
}