I log starting "when the airplane moves under its own power for the purpose of FLIGHT", and ending when it "comes to rest after landing". If the engine is still running, it's not at rest...
...The plane is back "at rest" while you're fueling, and at no point in between when it first "moved under its own power" and when it came back to rest did you intend to fly. So, not loggable.
You* get into some really weird scenarios trying to follow the letter of the FAR's.
Safety issues aside, you could in theory start your engine, taxi to the fuel pumps, keep the engines running, refuel and go flying and meet the FAR requirement of moving under its own power for the purpose of flight and your definition that the plane is not at rest while the engine is running... But wait! Even if we drop that definition and say while the engine was running the plane came to rest and is at rest anytime it comes to a complete stop... how can I log time?
Ok... so then you can Start the engine, taxi to the runway, doing run-up during taxi, take off, do a lap around the pattern land, continue the ground roll to the fuel pumps before killing the engine... Refuel, hop back in the plane, restart and taxi for takeoff before continuing on the planned flight and log all of my time as "moving under its own power for the purpose of flight until the plane is back at rest" as long as you never let the plane stop rolling.
The issue also has a whole bunch of other oddities that can be applied... If the fuel pumps are in the direction which you need to go to reach the runway, what portion of the motion to the fuel pumps is for the purpose of getting fuel and what portion is intended for the purpose of flight? You're not going to start your engine, taxi to the fuel pumps, stop & refuel and then taxi back to parking just so you can confirm that all time logged was "for the purpose of flight" are you?
Of course if the fuel pumps are on the opposite side of the field than you might have a point but even in that case you should only "lose" the portion of the taxi from parking to the fuel pumps... The return trip past parking to the other side of the field is "taxiing for the purpose of flight."
Ultimately, it begs the question to what end does it really matter? In most places your taxi to fuel is likely going to be <6 minutes which is less than 0.1 on the hobbs which only measures in tenths of an hour. In other words, its a non-significant digit. Maybe if you were at DFW and had to taxi from 35R to 13R which could conceivably take 6 miles and 2 hours at a CDC defined fast walk of 3-4 mph (does anyone actually taxi at that speed?) it would be a significant difference but that's normally why larger airports are designed with the ramp being located somewhere near the center of the field.
DFW is designed this way, so taxing to the fuel pumps would be "enroute" from 35R to the departure runway of 13R so almost all of those 2 hours on the ground taxiing at DFW could be the for "the purpose of flight" even with the stop. Of course, you'd realistically never have to make such a long and arduous taxi journey.
As to abuse? There will always be someone who tries to abuse the system. Rules are usually put in place to curb the most excessive and blatant abuses but once a rule has been established and written down, it defines what is "technically" acceptable and there will always be someone who tries to test the boundary of the definition of legal. Language lacks sufficient descriptive power to adequately define all scenarios. That's usually how new rules or in the case of the FAA, interpretations, come about... Someone trying to work the system to their advantage (or rat out someone working the system to their advantage). Its also how most scandals come about, getting caught doing something within the bounds of the law but which nobody else considered such an application (the size of the scandal often is directly proportional to the cognitive dissonance exhibited and the population that failed to consider the implication... i.e. the NSA spies on allied foreign leaders?!?)
I find it particularly funny that a person** who made a moderately personal rebuke of my own application of a "legal intent, erring in the direction of safety" based definition of a term not explicitly defined by the FAA though implicitly accepted as part of the international is making their own "intent" based argument here to support their own methodology of logging time. Arguing "flight time" is only the time while the plane is in the air is inconsistent with the explicitly defined definition of flight time by the FAA as "when an airplane moves under its own power for the purpose of flight and ending when it comes to rest after landing"
*Note: I use "you" in the broadest sense possible not as a personal point of contention with what
@flyingcheesehead said. The included quote however does help highlight the absurd realities of the FAR.
**Also not flyingcheesehead.