duikkie wrote:why not use a cheaper resistor
You can, but at the expense of predictability. This means you can get away with it in a totally sealed product (like a light bulb - where you're using something like a capacitive dropper anyway), but you probably can't anywhere that you have to be accurate for the fault current.
In the case of a power supply, you want accurate response to overload - if you overheat the windings, you risk burning off the insulation, and having full mains voltage flow across the transformer. Yes, you could use a transformer that can handle the greater current, but that's a lot more expensive, bulkier and heavier than a fuse.
This also suggests why it's undesirable for people to be able to replace the fuse...once the fuse goes, you've almost certainly had a fault, and there's a distinct chance that various other components that the safety of the user relies on may also be compromised.
The other thing I forgot to mention is that, particularly in 220/230/240V countries, a single resistor may not have the voltage rating for the supply - an 1/8W resistor is perhaps 200V, and a 1/4W 250V. Depending on where it is in the circuit, that might, or might not be acceptable.
Remember in all of this, that there's not necessarily someone watching the device.
topcat96 wrote:Different countries have different rules and regulations in regards to electrical equipment. Maybe they used a fuse to comply with as many as possible.
Sort of; the compliance regime differs (in both focus and rigidity of application), but safety of household appliances (for instance) is IEC 60335, so, the rules are, essentially, a worldwide requirement. The specific per country law usually just requires that it's 'as safe as it reasonably can be' or points to 'relevant international standards'. Adherence to standards like IEC 60335 is, of course, an excellent way of demonstrating due diligence.
Examples of non-members/affiliates of the IEC are North Korea, Somalia and the Solomon Islands. However, it's likely there are equivalent requirements in the vast majority of non-members - for instance the Solomon Islands require designers, manufacturers, importers and suppliers, 'to ensure, so far as is reasonably practicable, that the article is so designed and constructed to be safe and without risks to health when properly used'. Again, compliance with international standards is a good way of demonstrating you did this.
 For instance, a table saw needs a spinning sharp blade (that could remove a hand) in order to work, however, it shouldn't allow sparks to ignite collected sawdust.