Why are KACV and KTLV depicted differently on sectional charts than KSGU, KBIH, and KTPL, even though each is E2 w/ E4 extensions?
It looks like the answer is "it's a mistake or inconsistency in the sectional charts".  Whether or not it's an outright mistake is debatable, but it certainly appears to be an inconsistency, and one can argue that the depiction used for KACV and KTLV provides some useful information that the depiction used for KSGU, KBIH, and KTPL does not.  

It is the case that at KTLV-- but not at KACV or the other 3 airports mentioned here-- the description of the E4 airspace in the "Airspace Designations and Reporting Points" document has a note to see the A/FD for effective hours, while the E2 airspace has no such note.  The sectional chart has a similar notation, with an arrow pointing specifically to the E4 airspace.  (It also is the case that the current A/FD entry for KTLV simply reads "Airspace: Class E".)  It seems possible that the policy of the charting agency is to depict the adjoined E2 and E4 Class-E-to-surface areas as two distinct areas in any case where there is a possibility why their effective hours may be different.  If this is true, it doesn't explain why that style of depiction was also used for KACV.