关于索引定界的疑问

我今天看了一个资料，资料上写的如果谓词是大于操作符，那么它不是范围界定谓词，如果谓词是大于等于操作符，那么它就是范围界定谓词。可是我实验发现不是这样子的啊！
语句1：select count(*) from test where id>500 and id<=1000
Access Table Name = DB2INST1.TEST  ID = 2,4
|  Index Scan:  Name = DB2INST1.IDX_TEST2  ID = 1
|  |  Regular Index (Not Clustered)
|  |  Index Columns:
|  |  |  1: ID (Ascending)
|  #Columns = 0
|  Avoid Locking Committed Data
|  #Key Columns = 1
|  |  Start Key: Exclusive Value
|  |  |  1: 500
|  |  Stop Key: Inclusive Value
|  |  |  1: 1000
|  Index-Only Access
|  Index Prefetch: Sequential(2), Readahead
|  Lock Intents
|  |  Table: Intent Share
|  |  Row  : Next Key Share
|  Sargable Index Predicate(s)
|  |  Predicate Aggregation
|  |  |  Column Function(s)
Aggregation Completion
|  Column Function(s)
Return Data to Application
|  #Columns = 1

End of section


Optimizer Plan:

   Operator
     (ID)   

    RETURN
     ( 1)  
     |   
    GRPBY
    ( 2)  
     |   
   IXSCAN
    ( 3)  
    |      
Index:   
DB2INST1  
IDX_TEST2

语句2：select count(*) from test where id>501 and id<=1000
Access Table Name = DB2INST1.TEST  ID = 2,4
|  Index Scan:  Name = DB2INST1.IDX_TEST2  ID = 1
|  |  Regular Index (Not Clustered)
|  |  Index Columns:
|  |  |  1: ID (Ascending)
|  #Columns = 0
|  Avoid Locking Committed Data
|  #Key Columns = 1
|  |  Start Key: Inclusive Value
|  |  |  1: 501
|  |  Stop Key: Inclusive Value
|  |  |  1: 1000
|  Index-Only Access
|  Index Prefetch: Sequential(2), Readahead
|  Lock Intents
|  |  Table: Intent Share
|  |  Row  : Next Key Share
|  Sargable Index Predicate(s)
|  |  Predicate Aggregation
|  |  |  Column Function(s)
Aggregation Completion
|  Column Function(s)
Return Data to Application
|  #Columns = 1

End of section


Optimizer Plan:

   Operator
     (ID)   

    RETURN
     ( 1)  
     |   
    GRPBY
    ( 2)  
     |   
   IXSCAN
    ( 3)  
    |      
Index:   
DB2INST1  
IDX_TEST2

看上面两个语句没有什么问题啊？在start key和end key方面都是差不多的啊！
test表的表结构如下：
Column name                     schema    Data type name      Length     Scale Nulls
------------------------------- --------- ------------------- ---------- ----- ------
ID                              SYSIBM    INTEGER                      4     0 Yes   
NAME                            SYSIBM    VARCHAR                     20     0 Yes