I am sure some may well be - like Stratocaster or Telecaster for example - let alone 'Les Paul'. 3 of the most 'iconic' instruments and they are all 'protected' names. No one but Fender can make a Stratocaster or Telecaster, no one but Gibson can make a 'Les Paul' or Flying V or Explorer...
Not everyone will protect the name of their Guitar but their Logo, their Headstock shape, even inlay style or 'body' shape is more likely to be Protected. I doubt Heritage would 'protect' the 'H-150' model name and most wouldn't even know the model name - to them, its a 'Heritage Les Paul'. Of course, Heritage can't call it that, but it doesn't make much sense to copyright or trademark the 'H-150' name and the headstock, the brand name etc are 'protected'.
Naming something after an already existing thing - like Kestrel for example maybe more difficult to trademark/copyright as its something that existed before the company chose to name their products after that Bird. However, if Emerald (or PRS - whichever came later) had made their 'Kestrel' as a bass guitar and/or designed their version to be 'similar', then you may have some 'Legal' right to protect your 'Kestrel Bass Guitar' line and/or accuse Emerald of 'deliberately' naming their Product the same to 'confuse' customers. With them being so different, you aren't going to go into a shop to buy a Kestrel Bass and coming out with an Archtop 6 string guitar.
I guess its very dependent on the origin of a model name and the company, whether they think its worth copyrighting or not. Obviously the 'Les Paul' was named after its 'co-designer' and endorser so being named after a specific 'person' is likely to be different to naming a guitar after a species of Animal - like Kestrel, Hawk, Eagle and even whether or not you can, could or should protect it. I can't see Ibanez names being protected either but there is 'enough' elements on their 'instruments' that are protected by trademarks, copyrights etc that someone can't make a 'copy' to confuse the consumer into purchasing something they thought was something else...
That's why PRS didn't lose their 'Single Cut' fight with Gibson because PRS had enough of their 'own' design, their own characteristics that even if you only saw them in silhouette, you could still tell which was the Gibson. The Birds are 'instantly recognisable as 'PRS' too so the judge ruled that no-one would walk into a Shop intending to 'buy' a Gibson Les Paul and walk out with a PRS by 'mistake' thinking it was a 'Gibson' because there are sufficient differences between them and a retailer isn't going to sell you a 'PRS' by mistake if you ask for a Gibson Les Paul. PRS may have some protection over the name 'Kestrel' - no other company can make a 'Bass' called Kestrel, but that doesn't stop a company calling their product Kestrel if its not a bass guitar.
I don't think there is a standard that 'every' company follows so if Gibson protect the name Explorer, then every company protects the name of their models too as they may feel that their 'brand' name, their Logo or some other 'identifying' trait (like Bird inlays) are more important and 'Protect' their design, their 'instrument' enough...